Rollup merge of #150445 - petrochenkov:keepscope, r=nnethercote

resolve: Preserve binding scopes in ambiguity errors

It allows to get rid of `AmbiguityErrorMisc`, `Flags` and `extern_prelude_flag_binding`.

Also keep all encountered bindings in `resolve_ident_in_scope_set`, it allows to get rid of `extern_prelude_item_binding`.

This also unblocks https://github.com/rust-lang/rust/pull/149681 because the newly preserved data will help to fix the regressions in https://github.com/rust-lang/rust/pull/149681#issuecomment-3679059703 in a reasonable way.