Fix event queue being stuck in non-RTOS mode, causing all sorts of weird behavior

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: Remove mbed.h stub from target_h ...

The header `mbed.h` is a convenient wrapper that pre-includes some
platform headers, for use by user applications. Libraries and tests
internal to Mbed OS should not use it, and they should explicitly
include headers they need. So a stub is not needed.

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.

CMake: unittests: Remove trailing whitespace

equeue: Enable use of stub from C++ ...

Add extern "C" to the equeue_stub declaration to avoid an error when a C
file implements the equeue_stub symbol (as we do in equeue_stub.c).

    Undefined symbols for architecture x86_64:
      "_equeue_stub", referenced from:
          Test_LoRaWANTimer_start_Test::TestBody() in Test_LoRaWANTimer.cpp.o
    ld: symbol(s) not found for architecture x86_64
    clang: error: linker command failed with exit code 1 (use -v to see invocation)

cmake: Avoid linking to gcov ...

Use the `--coverage` option instead of manually linking to gcov, as some
host platforms (like macOS, FreeBSD) don't have gcov by default and use
an llvm equivalent instead.

equeue: Add missing header guards ...

The header equeue_stub.h was missing header guards to enforce single
inclusion. Add some header guards.

CMake: Move events fakes into events double dir ...

Previously events fakes as part of UNITTESTS/fakes, this PR moves
events fakes to events double directory to make events stubs
to be self-contained.

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

Previously the events 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: Move events stub headers to the events/tests/UNITTESTS/double dir ...

Move events stubs headers to the mbed-os/events/tests/UNITTESTS/double
directory and update double CMake to include stub headers

CMake: unit-tests: Move mbed-headers-events to the events directory ...

Move the header-only mbed-headers-events library the unit test stubs
depend on into the events component directory. This makes the events
stubs more self-contained and improves the composition of the library.

CMake: Move events stubs sources to the mbed-os/events directory ...

Move the events stub into the events component directory.
so we can avoid duplicating the mbed-os source tree in a central
UNITTESTS folder.

events-timing test should not need any LED1

Merge pull request #14828 from hazzlim/add-cmake-supports-psa-tests ...

CMake: Add CMake to mbed-psa greentea tests

CMake: Require TEST_SOURCES in greentea CMake file ...

Assumption that greentea test file is always named main.cpp is
incorrect. Updated mbed_greentea_add_test() macro to make TEST_SOURCES
parameter compulsory, which is used to specify greentea test
file(s). This allows tests to use C, or have a different name.
Therefore also updated all pre-existing greentea test CMake files to
explicity add main.cpp to TEST_SOURCES.

CMake: unit-tests: Make events UNITTESTS only depend on headers it uses ...

Previously the events unit tests 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: Remove all unittest.cmake script from test suite ...

- Remove redundant cmake script as already added the CMake configuration file
- Remove redundant empty_baseline as it is no longer needed with the help of CMake configuration file

CMake: Refactor event unittest cmake ...

- Added CMake configuration file into events unittests

Merge pull request #13975 from adbridge/eventq ...

Update EventQueue API to use chrono times

Tweak events API update and update Greentea tests accordingly

CMake: rename greentea test macro

Merge pull request #14087 from adbridge/events ...

Update events period method to check for invalid values

Minor formatting tweak to fix file permissions

Revert "one final whitespace change!" ...

This reverts commit c9a3375.

one final whitespace change!

Fix whitespace to stop astyle complaining

Remove unecessary namespace qualified ...

(Also minor whitespace correction)

Apply suggestions from code review ...

Co-authored-by: Hugues Kamba <41612201+hugueskamba@users.noreply.github.com>

Fix some whitespace issues