Bluetooth: Audio: Media control BabbleSim tests

This commit add the BabbleSim tests for the media control client, the
media control service and the media proxy.  This is a part of the
upmerge of the le-audio media control files.

These tests have been developed and maintained along with the media
control functionality.  The tests are believed to cover all
implemented media control functionality.

The commit is a pure copy of the files and content in the
topic-le-audio branch, with the exception that some include paths have
been modified to correspond to new locations of files and that the
tests have been guarded with ifdefs.

Signed-off-by: Asbjørn Sæbø <asbjorn.sabo@nordicsemi.no>

test guards