Rollup merge of #143657 - LorrensP-2158466:split-macro-map, r=petrochenkov

Resolver: refact macro map into external and local maps

Puts `MacroData` inside of the `ResolverArena` and splits `macro_map` into 2 maps: `local_macro_map` and `external_macro_map`. This way `get_macro_by_def_id` can take a `&Resolver` instead of a mutable one.

Part of [#gsoc > Project: Parallel Macro Expansion](https://rust-lang.zulipchat.com/#narrow/channel/421156-gsoc/topic/Project.3A.20Parallel.20Macro.20Expansion/with/516965603)

r? `@petrochenkov`

Author: matthiaskrgr