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.
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().