Auto merge of #43826 - kennytm:fix-43796-mis-calculated-spans, r=petrochenkov

Auto merge of #43826 - kennytm:fix-43796-mis-calculated-spans, r=petrochenkov

Fix "Mis-calculated spans" errors from `-Z save-analysis` + refactoring

Removed the path span extraction methods from `SpanUtils`:

* spans_with_brackets
* spans_for_path_segments
* spans_for_ty_params

Use the `span` fields in `PathSegment` and `TyParam` instead.

(Note that since it processes `ast::Path` not a qualified path (`hir::QPath` / `ast::QSelf`), UFCS path will be flattened: `<Foo as a::b::c::Trait>::D::E::F::g` will be seen as `a::b::c::Trait::D::E::F::g`.)

Fix #43796. Close #41478.

r? @nrc