Auto merge of #56759 - petrochenkov:prestabuni, r=nikomatsakis

Auto merge of #56759 - petrochenkov:prestabuni, r=nikomatsakis

Stabilize `uniform_paths`

Address all the things described in https://github.com/rust-lang/rust/issues/56417.

Assign visibilities to `macro_rules` items - `pub` to `macro_export`-ed macros and `pub(crate)` to non-exported macros, these visibilities determine how far these macros can be reexported with `use`.

Prohibit use of reexported inert attributes and "tool modules", after renaming (e.g. `use inline as imported_inline`) their respective tools and even compiler passes won't be able to recognize and properly check them.

Also turn use of uniform paths in 2015 macros into an error, I'd prefer to neither remove nor stabilize them right away because I still want to make some experiments in this area (uniform path fallback was added to 2015 macros used on 2018 edition in https://github.com/rust-lang/rust/pull/56053#issuecomment-441405140).

UPDATE: The last commit also stabilizes the feature `uniform_paths`.

Closes https://github.com/rust-lang/rust/issues/53130
Closes https://github.com/rust-lang/rust/issues/55618
Closes https://github.com/rust-lang/rust/issues/56326
Closes https://github.com/rust-lang/rust/issues/56398
Closes https://github.com/rust-lang/rust/issues/56417
Closes https://github.com/rust-lang/rust/issues/56821
Closes https://github.com/rust-lang/rust/issues/57252
Closes https://github.com/rust-lang/rust/issues/57422