Bluetooth: Audio: Media control shell commands

This commit adds shell commands for the media control client, the
media player and the media proxy.  This is a part of the upmerge of
the le-audio media control files.

The commit is a pure copy of the files and content in the
topic-le-audio branch, with these exception:

- some include paths have been modified to correspond to new locations
  of files.
- some instances of the shell variable has been renamed to not be the
  same as the name of the shell struct tag.
- spaces have been replaced with TABs a couple of places
- remove cplusplus guards
- changed a debug dependency for MCC from MCS to MCC
- changed log name for the media controller shell

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

mcc.c shell - replace name of shell variable

tmp

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shell