Rollup merge of #151142 - SpriteOvO:type-info-adt, r=oli-obk

Support ADT types in type info reflection

Tracking issue: rust-lang/rust#146922 `#![feature(type_info)]`

This PR supports ADT types for feature `type_info` reflection.
(It's still a draft PR, with implementation in progress)

Note that this PR does not take SemVer into consideration (I left a FIXME comment). As discussed earlier ([comment](rust-lang/rust#146923 (comment))), this requires further discussion. However, I hope we could get an initial implementation to land first, so we can start playing with it.

### Progress / Checklist

- [x] Struct support.
- [x] Enum
- [x] Union
- [x] Generics
- [ ] ~Methods~ Implemented and to be implemented in other PRs
- [ ] ~Traits~ Implemented and to be implemented in other PRs
- [x] Rebasing PR to `main` branch
  ~~(It's currently based on PR rust-lang/rust#151123, so here's an extra commit)~~
- [x] Cleanup and Rebase.
- [x] Fix field info for references. (see [comment](rust-lang/rust#151142 (comment)))

r? @oli-obk

Author: Urgau