Parse unparenthesized half-open range patterns inside slice patterns

[dtolnay]

• Tracking issue: Tracking issue for ..X, and ..=X (#![feature(half_open_range_patterns)]) rust-lang/rust#67264
• Feature gate: #![feature(half_open_range_patterns_in_slices)]

https://github.com/rust-lang/rust/blob/be01dabfefd2daa4574b974f571c7852085d60cb/tests/ui/consts/miri_unleashed/const_refers_to_static_cross_crate.rs#L42C9-L42C25

match x {
    &[1..] => {}
    _ => {}
}

Syn currently rejects this syntax.

error: range pattern is not allowed unparenthesized inside slice pattern
  --> tests/ui/consts/miri_unleashed/const_refers_to_static_cross_crate.rs:42:12
   |
42 |         &[1..] => false,
   |            ^^