Add section on method resolution regarding supertrait shadowing

[Amanieu]

Stabilization PR: rust-lang/rust#148605
Tracking issue: rust-lang/rust#89151

[ehuss]

@yaahc I am assuming the ambiguities regarding paths for this feature would fall under your work for type-dependent name resolution?

[yaahc]

I believe you're correct, tho I'm not 100% sure. I've been viewing type-relative name res and method res as separate processes and haven't dug super deeply into method/probe.rs which is where this logic lives afaict. Earlier when I was digging through resolve_fully_qualified_call and saw that it invokes method probing in "Path Mode" which is a significantly abbreviated set of steps compared to method resolution I stopped digging deeper.

• https://github.com/rust-lang/rust/blob/main/compiler/rustc_hir_typeck/src/method/probe.rs#L256-L258
• https://github.com/rust-lang/rust/blob/main/compiler/rustc_hir_typeck/src/method/probe.rs#L407

Given that method resolution already has it's own section, my plan so far has been to document what type-relative resolution is and when it applies, and for the cases where it overlaps with method resolution I was going to document how it differs from method resolution rather than reiterate the applicable steps so we'll only have a single source of truth to maintain.