VS2 doesn't support the latest MC. It's time to fix that.

Goals:

1. Initial port to 1.21, get everything functioning
2. Fix mixins to vanilla mc
3. Fix mixins to mods that have 1.21 equivalents

I'll be updating this issue as I make progress.

I won't make a branch for it until #1048 is done.

Maybe after Create supports 1.21+

Please update, that would be amazing!
Don't wait for create.