Auto merge of #47657 - algesten:save-analysis-impls, r=nrc

Auto merge of #47657 - algesten:save-analysis-impls, r=nrc

Emit data::Impl in save-analysis

As discussed on [internals.rust-lang](https://internals.rust-lang.org/t/rustdoc2-rls-analysis-and-the-compiler-help-wanted/6592/5), this PR emits `rls-data::Impl` in the save-analysis.

A number of questions are outstanding:

- [x] A few `???` around row 356. We need to discuss what goes here, if anything.
- [ ] ~~Deriving `id` for impl using hashing. Is this going to clash with rustc defids?~~
- [ ] ~~Deriving `id` for impl using hashing. Is the conversion from 64 bit -> 32 bit problematic?~~
- [x] Need a new rls-data with an `id` field in `Impl` struct.
- [ ] ~~Need a new rls-data which `derive` `Hash` for `ImplKind` enum.~~