Scan Bitwig default content location for wavetables

[baconpaul]

Over in #7694 we had a long convo about the wt spec, leading to fix to surge to load wt16 properly
Bitwig wt are all int16 content and I used them to test.

They live in (by default)

Linux: $HOME/.BitwigStudio/installed-packages/
Windows: C:\Users\bique\AppData\Local\Bitwig Studio\installed-packages
macOS: ~/Library/Application\ Support/Bitwig/Bitwig\ Studio/installed-packages

where of course AppData should be %LOCALAPPDATA% and Library should be the OS blah blah. You know the drill.

Anyway we could look for those and recurse them and make a folder for WT like Bitwig Content/ with sub-folders underneath if we find the dir and it has WTs, and then voila surge suers with bitwig would get all their bitwig content available, if they have not changed the content location.