3591: Support local macro_rules r=matklad a=edwin0cheng
This PR implement local `macro_rules` in function body, by adding following things:
1. While lowering, add a `MacroDefId` in body's `ItemScope` as a textual legacy macro.
2. Make `Expander::enter_expand` search with given `ItemScope`.
3. Make `Resolver::resolve_path_as_macro` search with `LocalItemScope`.
Fix#2181
Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>