RBS for Ruby 3.3

[soutaro]

I want to release RBS 3.4 bundled with Ruby 3.3.

1. We may postpone major changes to RBS 3.5, to avoid making the codebase unstable and ensure dependencies (irb, typeprof) work with Ruby 3.3
2. Signature updates to be included in RBS 3.4 assumes Ruby 3.3 -- incompatibilities caused by Ruby 3.3 can be skipped in the test

[soutaro]

RDocs copied into RBS files may cause problems. I will take care of updating them before Ruby 3.3. Continue working with Ruby 3.2 docs.