typeck: use a TypeVisitor in ctp

[arielb1]

Use a TypeVisitor in ctp instead of ty::walk

This fixes a few cases where a region could be projected out of a trait while not being constrained by the type parameters, violating rust-lang/rfcs#447 and breaking soundness. As such, this is a [breaking-change].

Fixes #35139

r? @eddyb

[eddyb]

@bors r+

[bors]

📌 Commit 0a128f3 has been approved by eddyb

[bors]

⌛️ Testing commit 0a128f3 with merge 7333c4a...

[eddyb]

Crater report shows 1 root regression: owning_ref.

cc @rust-lang/lang

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-cargotest, auto-linux-64-cross-freebsd, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-mir, auto-linux-64-opt-rustbuild, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-opt, auto-mac-64-opt-rustbuild, auto-mac-cross-ios-opt, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-cargotest, auto-win-msvc-64-opt, auto-win-msvc-64-opt-mir, auto-win-msvc-64-opt-rustbuild
Approved by: eddyb
Pushing 7333c4a to master...

[nikomatsakis]

Given the minimal impact, this doesn't require a warning period, but we still ought to do our best to minimize impact before landing and help users. e.g. give an explanatory note on the error indicating that there was a recent bug-fix (it'd be ok, I think, for that note to appear even if the error would have happened before), and/or submit a PR to fix the problem. Still, given that this landed, I'm not inclined to roll it back. Just saying.

cc @Kimundi -- this change fixes a hole that the "owning-ref" crate was relying on.