Support 2021 Edition `pat` matcher in `macro_rules`

[jonas-schievink]

When a macro is defined in an edition 2021 crate, the :pat matcher should match "pattern_top" instead of "pattern_single", which allows or-patterns. :pat_param will match "pattern_single" in all editions.

[jonas-schievink]

Since this requires knowing the crate edition in some rather annoying places, I'd like to wait with this until the edition-dependent lexer changes in #9056 are implemented upstream, since that might already give us the required info

[Veykril]

We should prioritize fixing this now, as this is being used by the matches macro soon, rust-lang/rust#108829