docs: Update to reflect Mbed CLI 2 changes ...

Due to the recent release of Mbed CLI 2, the command line options
have been renamed to ensure good usability and harmonize with the old
tools.

These are the following changes done:
* Minimum Cmake - 3.19.0 is required
* Minimum Mbed-tools - 4.0.0 is required
* mbed-tools cmd `init` to `new`
* mbed-tools cmd `build` to `compile`
* Removed whitespaces

CMake: Rename Mbed OS path variable for consistency ...

Rename the CMake variable expected from applications from MBED_ROOT to
MBED_PATH to be consistent with the naming used for the configuration file
(MBED_CONFIG_PATH) also expected from applications.

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: Componentize Mbed OS into multiple CMake targets (#13732) ...

Aside from the core mbed-os CMake target, a number of targets have been created so they can optionally be included by application executables that require them using `target_link_libraries()`.

Co-authored-by: Martin Kojtal <martin.kojtal@arm.com>
Co-authored-by: Rajkumar Kanagaraj <rajkumar.kanagaraj@arm.com>

CMake: Add support for printf lib selection

CMake: Add support for C lib selection ...

Configure the selected toolchain for the selected C library

CMake design: update to the latest version of feature-cmake branch (#13614) ...

We made changes like tools/cmake folder change, removed app.cmake.

CMake design doc: update to the latest mbed-tools updates ...

Refactor Mbed OS CMake scripts section - details about mbed-os/cmake scripts
Add mbed-tools - how mbed-tools built an application with CMake

CMake: Add design document