- Split mbed-core and mbed-rtos into -sources and -flags targets ...

- Fix some logic errors in top level cmakelists related to building greentea tests
- Fix mbed_create_distro() for OBJECT libraries

CMake: add mbed-os and mbed-baremetal targets ...

mbed-os consists of mbed-core and mbed-rtos
mbed-baremetal consists of mbed-core

The main change is for mbed-core. Changing from object library to be interface. This way it allows us to do the above to have 2 main targets for users to use.

This should be backward compatible change as mbed-os target we used contains the same files/options as previously set.

CMake: Rename CMake targets ...

* mbed-os renamed mbed-core
* mbed-os-<COMPONENT> renamed mbed-<COMPONENT>

CMake: replace usage of the mbed_add_cmake_directory_if_labels() function (#13754) ...

Directories that start with special prefixes (TARGET_, FEATURE_, COMPONENT_)  are added to the build based on Mbed target configuration from targets.json instead of calling utility function mbed_add_cmake_directory_if_labels().

CMake: Fix build due to hal dir move

Refactor hal directory

Move USB Templates to `mbed-os/hal/usb`

USB public APIs cleanup (#11034) ...

The contents of the usb directory were moved to appropriate locations and the usb directory removed.

* Public USB headers moved under drivers/
* Internal USB headers moved under drivers/internal/
* USB Source code moved under drivers/source/usb/
* Moved usb/device/hal/ under hal/usb/
* Moved usb/device/USBPhy/ under hal/usb/
* Merged usb/device/targets/ into targets/
* Separated public and private USB API documentation under Doxygen groups drivers-public-api and drivers-internal-api.