This was the last player class.
This code was also cleaned up for non-Windows systems where CD Audio is not implemented.
Instead of providing an empty implementation, all related code is now explicitly deactivated.
It is now being handled by the controlling code.
While of no benefit for GZDoom itself, this finally allows to separate the entire music code into a separate, engine independent project that merely provides streamed music data when not playing on a hardware device (WinMM Midi or CD Audio.)
The tight coupling of the music code with the sound backend made this nearly impossible before
This was getting a bit unwieldy. The include path setup is not perfect yet, that's work for later.
(It's about time we're getting C++20 with modules so that this include path madness can be put to an end.)
Also made the decode_vorbis function in DUMB a function pointer so that the library does not depend on high level code and can just ignore the vorbis case if no supported.
