Match ergonomics 2024: align implementation with RFC
- Remove eat-two-layers (`ref_pat_everywhere`)
- Consolidate `mut_preserve_binding_mode_2024` into `ref_pat_eat_one_layer_2024`
- `&mut` no longer peels off `&`
- Apply "no `ref mut` behind `&`" rule on all editions with `ref_pat_eat_one_layer_2024`
- Require `mut_ref` feature gate for all mutable by-reference bindings
r? ``@Nadrieril``
cc https://github.com/rust-lang/rust/issues/123076
``@rustbot`` label A-edition-2024 A-patterns