Change google test git tag to main ...

google test changed from master to main branch

CMake: Move ble fakes into FEATURE_BLE double dir ...

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

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 #14765 from rwalton-arm/fix_unittest_check ...

Fix unittest check

CMake: unit-tests: Fetch googletest master ...

googletest now follows the "Abseil Live at HEAD" philosophy, which means
they recommend using the latest commit on the master branch and always
compiling from source. They recommend this to avoid version mismatch
issues and "diamond dependency" problems which are common in dependency
graphs with pinned versions. Google make the "promise" that future
changes won't break downstream code if it follows the "Abseil
compatability guidelines".

Upping the version to master also fixes some CMake configure time
warnings that were present with the older tagged releases of googletest:

CMake Deprecation Warning at __build/_deps/googletest-src/CMakeLists.txt:4 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

CMake Deprecation Warning at __build/_deps/googletest-src/googlemock/CMakeLists.txt:45 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

CMake Deprecation Warning at __build/_deps/googletest-src/googletest/CMakeLists.txt:56 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

add fake event queue for unittests

CMake: Update mbed os, unittest CMake and add CMAKE_CROSSCOMPILING guard ...

- Add a new MbedOS project in mbed os root CMake which can be used along with
  BUILD_TESTING conditional check for enabling the unittest build
- Update UNITTEST CMake for setting the CMake configuration like c, cxx flags etc.,
- Add if CMAKE_CROSSCOMPILING conditional check wherever target configuration check
  and toolchain configuration to avoid such configuration gets included for unittest build.

Update UNITTEST for kvstore

Move mbed-trace into platform

Update UNITTESTS header reference

Fix UNITTESTS build failure

Incorporating review comments

Mbed OS will soon be changing directory structure to the below: ...

```
connectivity
├── netsocket
├── lorawan
│   ├── mbed_lib.json // nanostack-interface's mbed_lib.json
│   ├── lorastack
│   ├── tests
├── nanostack
├── cellular
├── ...

```

This PR is a part of a wider \connectivity refactoring and implements the above new directory structure for \lorawan.

Update mbedtls paths

Merge pull request #13298 from ashok-rao/platform-refactor ...

Refactoring \platform directory

Fixing .astyleignore conflict

Move drivers unit tests

Relocate platform unit tests

Restructure events directory & move tests

Merge pull request #13335 from rajkan01/netsocket_dir_restructure ...

Restructure netsocket directory

Merge pull request #13307 from rajkan01/storage_kv_dir_resturcture ...

Restructure storage kvstore directory

Update netsocket header and source reference in other libraries

Update unittest.cmake files for cellular

Update paths to cellular framework

Update greentea config, header reference

Merge pull request #13300 from rajkan01/storage_fsdir_restructure ...

Restructure storage filesystem directory

Merge pull request #13264 from ashok-rao/rtos-refactor ...

Moving around a few items within \rtos

Fix UNITTESTS issue

Move greentea test closure to library

Merge pull request #13273 from rajkan01/storage_rb_dir_restructure ...

Restructure storage blockdevice directory