Auto merge of #47791 - estebank:mismatched-trait-impl, r=nikomatsakis

Tweak presentation on lifetime trait mismatch

 - On trait/impl method discrepancy, add label pointing at trait signature.
 - Point only at method definition when referring to named lifetimes on lifetime mismatch.
 - When the sub and sup expectations are the same, tweak the output to avoid repeated spans.

Fix #30790, CC #18759.

diff --cc src/librustc/infer/error_reporting/mod.rs
Simple merge

diff --cc src/test/ui/issue-46472.stderr
Simple merge