Rollup merge of #140036 - jieyouxu:ui-cleanup-4, r=compiler-errors

Advent of `tests/ui` (misc cleanups and improvements) [4/N]

Some `tests/ui/` housekeeping, to trim down number of tests directly under `tests/ui/`. Part of #133895.

### Review advice

- Best reviewed commit-by-commit.
- I can squash commits before merge, commits are separate to make it easier to review.

Author: ChrisDenton