Support or-patterns (`pat_0 | ... pat_n`) in nested positions

[Centril]

Tracking issue: rust-lang/rust#54883
RFC: rust-lang/rfcs#2535

The implementation history is available in the tracking issue, and I'm available if there are questions.

[bjorn3]

fn foo(x: Option<u8>) {
    match x {
        Some(0 | 1..=255) | None => {}
    }
}

parses fine.