Split frontend into smaller packages

[bates64]

Motivation: https://github.com/decompme/decomp.me/pull/739#issuecomment-1537380288

I also propose we shift to using pnpm instead of yarn when making this change, because pnpm is faster and more disk space efficient.

[bates64]

Must also investigate https://turbo.build/repo - we can cache builds in the cloud