Auto merge of #46532 - est31:master, r=est31
Allow feature-gate tests to live in ui/ and migrate most of the tests from compile-fail
The PR consists of three commits:
1. change tidy to allow feature-gate tests to live in ui/
2. migrate some feature gate tests to ui/ with renaming only
3. migrate some feature gate tests to ui/ with also removing `// gate-test-...` lines and renaming them to the standard `feature-gate-<feat-name>.rs` format.