Auto merge of #117578 - compiler-errors:derive-encode-in-rustc_type_ir, r=davidtwco

Derive `TyEncodable`/`TyDecodable` in `rustc_type_ir`

when `derive(TyEncodable)` or `derive(TyDecodable)` sees an `I` type parameter on a struct that has no `'tcx`, then parameterize the `TyEncoder`/`TyDecoder`'s interner over that variable rather than `TyCtxt<'tcx>`.

Also, emit where clauses for fields rather than generics.

Author: bors