- 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

Move ns_trace.h to mbed-trace folder

tr_array: fix use after free error after mbed_trace_free() is called ...

If one called mbed_trace_free() but continued using the trace (which
is a supported use case), the already freed tmp_data buffer was used
by tr_array().

This was spotted by Valgrind on some unit tests which do enable the
trace only temporarily for some of the tests.

Error being fixed in this PR:
--8<--8<--8<---
==5865== Invalid write of size 1
==5865==    at 0x2639BB: mbed_trace_array (mbed_trace.c:569)
<...>
==5865==  Address 0x5dc79d0 is 0 bytes inside a block of size 128 free'd
==5865==    at 0x4C32D3B: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5865==    by 0x262723: mbed_trace_free (mbed_trace.c:192)
<...>
==5865==  Block was alloc'd at
==5865==    at 0x4C31B0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5865==    by 0x262548: mbed_trace_init (mbed_trace.c:162)
<...>

Trace: Change tr_debug color from gray to bright blue ...

The gray-on-black color code used for debug level print-out in
mbed_trace is hard to read. Bright-blue-on-black increases the
brightness of the text without over shadowing the info level
default (white-on-black), thus making it easier to read while
maintaining the original intention.

For original color set MBED_TRACE_COLOR_THEME to 1.

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: Revert mbed-trace CMake input source file to match upstream repository (#13590) ...

As there is currently no mbed-trace library, statements related to that
target have been commented out.

CMake: Fix build failure due to mbed-trace, mbed-client-randlib, and nanostack dir changes

CMake: Add support for features dir

mbed-trace: if fea-ipv6 is null, check nanostack-libservice availability

Add include/ path for mbed-trace

Move mbed-trace into platform