Fix all Doxygen errors and make any future errors fatal (#118) ...

* Start working on fixing doxygen warnings

* Upgrade doxyfile to Doxygen 1.9.1

* Clean up some unmatched groups and add some exclusions

* Fix docs for rtos::ThisThread not showing up

* Fix up KV store docs

* Fix incorrect @files, some more incorrect groups

* Fix lots of broken links

* Start fixing mbedtls groups

* Fix more mbedtls docs

* Fix remaining mbedtls files with missing or incorrect grouping

* Fix a huge amount of PSA docs errors

* Fix a few more mbedtls docs errors

* Fix __cplusplus not defined for docs, clean up call in callback typedef, fix some docs errors

* Fix some broken doc links in HAL headers

* Fix more PSA doc errors

* Fix some doxygen errors in networking code

* Fix lots of network related doc errors

* Try and fix some CI failures

* Use Doxygen Action instead of doxygen in Mbed container to get the right version

* Try removing docs check

* Add first part of doxygen action

* Add next part of doxygen action

* Fix yaml syntax error

* Add in license check fix

* Try using verbose scancode

* Fix some more docs issues, workaround scancode-toolkit#3179

* Clean up the LoRaRadio get_state() function on each implementation.  Also fix some other compile and doc errors.

* Fix all remaining doxygen errors

* Fix escaping, for realsies this time

* Remove Doxygen unsupported config options, fix some more get_status() declarations

* Fix some UNITTESTS build errors

* Fix one more compile error

* Another unittest error

Move unit test to match file

modify method signatures to pass astyle tests

modify AT_CellularDevice_stub to pass test with the new feature

Unit tests: Remove redundant CMake target mbed-headers-base ...

Individual libraries' `target_h` stub headers have now all been moved
from `mbed-headers-base` to `mbed-headers-<library>`.

Note: Even though headers previously in `target_h` are technically
stubs/fakes too, they are used by not only unit tests but also regular
libraries when compiled for unit tests, because no target-specific HAL
implementation exists in this case. In order for regular library
sources to pick up `target_h` headers, those headers must

* have the same names as regular headers
* appear first in include paths

This is why those headers are part of `mbed-headers-<library>` and not
`mbed-stubs-<library>`. Before this refactoring, `mbed-headers-base`
was the first in unit tests' include paths.

Unit tests: Fix style in cellular myCellularContext.h stub

Unit tests: Move cellular target_h stubs ...

We move test-specific files from the top-level UNITTESTS directory
into individual components' UNITTESTS/doubles subdirectories.

unittests: Remove ATHandler test interdependencies ...

Some tests in athandlertest.cpp relied on the state of stubs set in
previous tests. This caused test failures if the tests cases were ran in
isolation. Remove the interdependencies between tests by setting stub
values in the tests that rely on them.

CMake: unittests: Show all tests in CTest report ...

Previously a test executable was recognised as a single test by CTest.
However, test executables usually contain multiple test cases, the
results of the test cases should be individually reported. With our
previous setup we could miss test case failures that didn't cause the
executable to return an error code.

This commit uses gtest_discover_test to discover all test cases in a
test executable. This enables CTest to match test passes and failures
from the googletest binary output.

Remove mbed-headers-connectivity ...

Moved all the headers out of mbed-headers-connectivity, and these changes remove
that headers lib reference from lorawan and cellular unit tests

CMake: Limit cellular device cmake to use mocks/sources what it depends ...

Update cellular device unit tests CMake depends on a mock, which is
required for the test instead of depending on the group of mbed-stubs,
mbed-headers, mbed_stub_headers, libraries.
Limit the cellular context unit test CMake target_sources to keep only
required sources

CMake: Limit cellular common unit tests to use mocks what it depends ...

Update cellular common unit tests CMake depends on a mock, which is
required for the test instead of depending on the group of
mbed-headers libraries.

CMake: Limit at cellular unittest to use mock what it depends ...

Update AT cellular unit tests CMake depends on a mock, which is required
for the test instead of depending on the group of mbed-stubs,
mbed-headers, mbed_stub_headers, libraries.

CMake: Add mbed-headers-nanostack-libservice library ...

Previously all nanostack libservice headers part of
mbed-headers-connectivity. This PR moves all the nanostack
libservice headers into newly added mbed-headers-nanostack-libraries.
This makes the nanostack libservice stubs more self-contained and
improves the composition of the library.

CMake: Remove mbed-stubs-rtos-headers library ...

- Previous changes moved all rtos stubs headers into mbed-stubs-rtos-headers
lib, but the decision to keep all stubs headers under the respective
component stubs library so moved all stubs rtos headers under
mbed-stubs-rtos and updated it depend component CMake
- Remove unnecessary add_definition call for UNITTEST as any of the stubs library
added from UNITTEST/CMakeLists.txt is not required this macro

Merge pull request #14873 from ARMmbed/move_connectivity_netsocket_stubs ...

Move connectivity netsocket stubs

Merge pull request #14773 from rwalton-arm/move_platform_stub ...

Move mbed-stubs-platform to the platform directory

Merge pull request #14884 from LDong-Arm/rm_UNITTEST_macro ...

Remove the `UNITTEST` macro from production code

Merge pull request #14835 from ARMmbed/move_stubs_cellular_headers ...

Move stubs cellular headers

CMake: Move netsocket stub headers to the netsocket doubles dir ...

Previously all the netsocket stubs headers under mbed-stubs-headers,
so this PR move all netsocket stubs headers under
netsocket/tests/UNITTESTS/double directory and update CMake to include
stubs headers into mbed-stubs-netsocket library to make netsocket stubs
to be self-contained.

CMake: Add mbed-headers-netsocket headers library ...

- Previously, all netsocket headers made as a part of the
mbed-headers-connectivity library. To make it easier to separate all
the netsocket headers into the separate mbed-headers-netsocket library
and keep them, as part of netsocket stubs CMake. This makes the
netsocket stubs more self-contained and improves the composition of the library.
- Update cellular, netsocket unit tests to link only with a mbed-headers-netsocket
library that it depends on instead of link with mbed-headers
which is a group of headers libraries.

CMake: Update netsocket, cellular unittest to use mbed-stubs-netsocket ...

Update netsocket and cellular unit tests to link with a mbed-stubs-netsocket
library that it depends on instead of link with mbed-stubs
which is a group of stubs libraries.

rtos: Remove UNITTEST macro from rtos ...

Production code should not contain any test-specific checks. Rather
than checking `UNITTEST`, unit tests can directly set
`MBED_CONF_RTOS_PRESENT=1` to make RTOS available for testing.

Note: The cellular ATHandler test also has `MBED_CONF_RTOS_PRESENT=1`
added because `ATHandler.cpp` contains a check of this variable.

CMake: unit-tests: Split platform headers out of mbed-stubs-headers ...

We have a central collection of "stub headers", which makes reasoning
about dependencies rather difficult, as it forces every stub library to
depend on all available stub headers. The standard approach would be for
each stub library to expose its public headers, and its dependents to
explicitly specify a dependency on the stub library containing the
headers it needs. This is a more modular design than creating a
header-only monolith library. Move the platform stub headers from this
central library into the mbed-stubs-platform library to increase
modularity.

mbed-stubs-connectivity now depends on the mbed-stubs-platform because
it requires some headers which were moved to mbed-stubs-platform.

Unit tests: Create mbed-headers-filesystem ...

Create a CMake target mbed-headers-filesystem to separate FileSystem
headers from the generic mbed-headers-storage. Update tests to use it.

CMake: Move cellular stub headers to the cellular/tests/UNITTESTS/double dir ...

Previously all the stubs headers under mbed-stubs-headers,
so this PR move all cellular stubs headers under
cellular/tests/UNITTESTS/double directory and update CMake
to include headers into mbed-stubs-cellular library to make
cellular stubs to be self-contained

CMake: unit-tests: Make cellular stub only depend on headers it uses ...

Previously the connectivity cellular stub library depended on
`mbed-headers`, which is a collection of all available headers
in mbed-os. To make it easier to separate the library, only depend
on the headers we're using.

CMake: unit-tests: Add mbed-headers-cellular headers library ...

- Previously all cellular header made as a part of the
mbed-headers-connectivity library. To make it easier to separate all
the cellular headers into the separate mbed-headers-cellular library
and keep them as part of cellular stub CMake. This makes the cellular
stubs more self-contained and improves the composition of the library.
- Update all unit test that depends on cellular headers with mbed-headers-cellular library

CMake: Move connectivity/cellular stubs to the mbed-os/connectivity/cellular dir ...

Move the connectivity cellular into the connectivity/cellular component
directory. So we can avoid duplicating the mbed-os source tree in a
central UNITTESTS folder.

Merge pull request #14819 from ARMmbed/move_rtos_stubs ...

Move rtos stubs to the rtos directory