Rollup merge of #52904 - pnkfelix:issue-51167-sort-by-span, r=petrochenkov

Rollup merge of #52904 - pnkfelix:issue-51167-sort-by-span, r=petrochenkov

NLL: sort diagnostics by span

Sorting the output diagnostics by span is a long planned revision to the NLL diagnostics that we hope will yield a less surprising user experience in some case.

Once we got them buffered, it was trivial to implement. (The hard part is skimming the resulting changes to the diagnostics to make sure nothing broke... Note that I largely rubber-stamped the `#[rustc_regions]` output change.)

Fix #51167