Auto merge of #53461 - petrochenkov:pmu, r=alexcrichton

resolve: Do not error on access to proc macros imported with `#[macro_use]`

This error is artificial, but previously, when `#[macro_use] extern crate x;` was stable, but non-derive proc macros were not, it worked like kind of a feature gate. Now both features are stable, so the error is no longer necessary.

This PR simplifies how `#[macro_use] extern crate x;` works - it takes all items from macro namespace of `x`'s root and puts them into macro prelude from which they all can now be accessed.