Rollup merge of #143742 - estebank:borrow-suggestion, r=compiler-errors

Rework borrowing suggestions to use `Expr` instead of just `Span`

In the suggestion machinery for borrowing expressions and types, always use the available obligation `Span` to find the appropriate `Expr` to perform appropriateness checks no the `ExprKind` instead of on the textual snippet corresponding to the `Span`. (We were already doing this, but only for a subset of cases.) This now better handles situations where parentheses and `<>` are needed for correct syntax (`&(foo + bar)`, `(&foo).bar()`, `<&Foo>::bar()`, etc.).

Unify the logic for the case where `&` *and* `&mut` are appropriate with the logic for only one of those cases. (Instead of having two branches for emitting the suggestion, we now have a single one, using `Diag::multipart_suggestions` always.)

Handle the case when `S::foo()` should have been `<&S>::foo()` (instead of suggesting the prior `&S::foo()`. Fix rust-lang/rust#143393.

Make `Diag::multipart_suggestions` always verbose. CC rust-lang/rust#141973.

Author: tgross35