Auto merge of #116830 - nnethercote:rustc_type_ir, r=compiler-errors

Remove `IdFunctor` trait.

It's defined in `rustc_data_structures` but is only used in
`rustc_type_ir`. The code is shorter and easier to read if we remove
this layer of abstraction and just do the things directly where they are
needed.

r? `@BoxyUwU`

Author: bors