WIP: Implement musicdef structs and music pre-loading

Goals:

Structure

Port musicdef code from Kart -- https://git.magicalgirl.moe/KartKrew/Kart-Public/merge_requests/23
Grab jingle list from musicplus-jingle
Add in-memory music data to musicdef

Change sound interface paradigm to load and unload music separately from playback
- ShutdownSound: Unload all music streams in the musicdef chain?
- LoadSong: On subsequent calls to LoadSong if the musicdef already has music loaded, check if we need to reload. Store a checksum of the previous lump?
Expose S_PreloadMusic(name, longevity) and S_UnloadMusic() method to Lua.
- longevity means keep permanently loaded, or unload upon map change, etc.
- Support "preload music" consvar by keeping a list of the requested names and their longevities. Refer to that list whenever the consvar changes.
Add "preload music" consvar and menu toggle, default on.
- Off means don't load any music into memory other than the current song.
- Add change handler: disable means unload all other songs. Enable means load the jingles and map names (see below)

Jingles are always loaded into memory
On each map load, search for the level header's music names, as well as music names for the Change Music linedef. Preload those songs.
When music lumps are replaced, check for current preloads. Reload the music that was replaced.