Rollup merge of #108133 - kylematsuda:earlybinder-cleanups, r=compiler-errors

Small cleanups around `EarlyBinder`

Cleaning up a few things that were brought up by `@lcnr` in reviewing #106696:

- [make `issue33140_self_ty` query return `Option<EarlyBinder<Ty>>`](rust-lang/rust#106696 (comment))
- [small style improvement](rust-lang/rust#106696 (comment))

Author: matthiaskrgr