Auto merge of #54743 - ljedrz:cleanup_ty_p2, r=zackmdavis

Cleanup rustc/ty part 2

The second part of cleanups and minor improvements for rustc/ty.
- improve allocations
- calculate span after a possible early continue
- simplify some patterns
- mark a comment as FIXME
- whitespace fixes

The PR is independent from from the first part.

diff --cc src/librustc/ty/fold.rs
Simple merge

diff --cc src/librustc/ty/instance.rs
Simple merge

diff --cc src/librustc/ty/item_path.rs
Simple merge

diff --cc src/librustc/ty/layout.rs
Simple merge

diff --cc src/librustc/ty/mod.rs
Simple merge

diff --cc src/librustc/ty/outlives.rs
Simple merge

diff --cc src/librustc/ty/structural_impls.rs
Simple merge

diff --cc src/librustc/ty/sty.rs
Simple merge

diff --cc src/librustc/ty/util.rs
Simple merge

diff --cc src/librustc/ty/walk.rs
Simple merge

diff --cc src/librustc/ty/wf.rs
Simple merge