Auto merge of #125782 - compiler-errors:supertrait-item-shadowing, r=BoxyUwU

Implement RFC 3624 `supertrait_item_shadowing` (v2)

Implements RFC 3624 and the associated lint in the RFC.

Implements:
* Shadowing algorithm
* Lint for call-site shadowing (allow by default, gated)
* Lint for definition-site shadowing (allow by default, gated)

Tracking:
- https://github.com/rust-lang/rust/issues/89151

cc `@Amanieu` and https://github.com/rust-lang/rfcs/pull/3624 and #89151