Rename inconsistently named testing-related variables. Also fix STM32CUBE not working from application code.

Convert storage/ targets into STATIC libraries

Clean up top-level build file and build options, fix build issues on MinGW

CMake: Add option to enable greentea tests ...

Add an option to enable the greentea tests independently from the unit
tests.

We can't just use the typical BUILD_TESTING option to enable greentea
tests. BUILD_TESTING enables unit tests and fetches googletest, which
are compiled for the host. Greentea tests are cross compiled and require
a toolchain file. For this reason we add a new option just to enable
greentea tests, preventing build failures triggered by the unit tests
and googletest.

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.

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

Merge pull request #14882 from LDong-Arm/storage_tests_cleanup ...

Unit tests: storage: Only use headers, sources and definitions needed by each test

Remove `#ifdef UNITTEST` from MbedCRC.h ...

Production code should not contain any test-specific checks. Rather
than checking `UNITTEST`, MbedCRC.h can simply include in all cases
<mstd_type_traits> whose unit test stub exists.

Also remove the `UNITTEST` macro from CMake definitions of kvstore
unit tests which depend on MbedCRC.h.

Unit tests: Make storage tests depend explicitly on headers it uses ...

The CMake target `mbed-headers` brings in all headers, and we are
gradually moving away from it and explicitly use only headers needed
by each unit test.

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

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

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.

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

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

Unit tests: Limit storage stubs to link what it uses

Move storage stubs into subdirectories of Mbed OS storage ...

Move storage stubs from UNITTESTS/stubs into components inside the
top-level storage directory. Specifically,
* storage/blockdevice/tests/UNITTESTS/doubles/ for BlockDevice stubs.
* storage/kvstore/filesystemstore/tests/UNITTESTS/ for a stub used by
the FileSystemStore test. The stub has been renamed from
kv_config_stub.cpp to filesystemstore_kv_config_stub.cpp, to make it
evident why it doesn't go into storage/kvstore/kv_config/.

CMake: Only build unit tests if Mbed OS is the current project ...

Typically when adding a unit test directory to a CMake project a check
will be used to ensure the subdirectory is added only if the following
are true:

* The BUILD_TESTING option is set to ON.
* The current CMake project is the top-level project.

The reason being, if a downstream project includes our project they
generally don't want to build our unit tests.

In mbed-os, we do correctly specify the above condition before adding
the central UNITTEST subdirectory, which fetches googletest and adds the
"stub" libraries the unit tests depend on. However, we only check if
CMAKE_CROSSCOMPILING is OFF (or undefined) before actually adding the
unit tests. This mismatched logic would lead to unexpected build
failures in various scenarios. One likely case could be: a downstream
project including mbed-os happens to set CMAKE_CROSSCOMPILING to
OFF/undefined for any reason (possibly to build its own unit tests).
mbed-os would go ahead and attempt to build its tests without fetching
googletest or adding the required stub targets.

To fix the issue replace the check for CMAKE_CROSSCOMPILING in the unit
tests with the same BUILD_TESTING idiom we use for adding the central
UNITTESTS subdirectory.

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 storage TDBstore and FileSystemStore unittest cmake ...

- Add CMake configuration file in TDBstore and FileSystemStore unittest.

CMake: Add add_subdirectory of unittests ...

- add every libraries unittest directory into respective CMake
  which allows to include unittest source into build based on
  MBED_BUILD_UNITTESTS flag

FileSystemStore unit test: remove erased_set_get test ...

The "erased_set_get" test case deinits `FileSystemStore`, erases the
block device, and reinits `FileSystemStore`. This of course fails,
because `BlockDevice::erase()` removes all stored data including the
format of the `FileSystem` (middle layer), unless the particular type
of block device has a no-op erase implementation.

Note: Previously `HeapBlockDevice::erase()` was essentially a no-op
so this test case did not fail. We recently added the freeing of heap
memory and it uncovered the problem.

KVStore: drop './' from CMake paths

Fix astyle in KVStore unit tests

KVStore: componentize CMake definitions into sub-components

Relocate kvstore Greentea tests into each store type's path

Relocate kvstore unit tests into each store type's path

Turn TDBStore and FileSystemStore into standalone libraries

Refactore storage/kvstore directory

Update header path reference

Update the header file reference

Storage directory restructure: ...

- Move mbed-os/features/storage to mbed-os/storage
- Move components/storage/blockdevice to storage/blockdevice/COMPONENT_xxx