Rollup merge of #152912 - HKalbasi:rustc_public_def_span, r=makai410

Expose Span for all DefIds in rustc_public

Part of rust-lang/project-stable-mir#118

To be maximally useful, `VariantDef` and `FieldDef` should be changed to be a wrapper around `DefId` instead of holding their parent and index. I can do this change in this PR or a follow-up if it is desired. For now, I added the missing `impl Stable for DefId` in internals so you can convert from rustc internals.

Author: JonathanBrouwer