Cleanup: Migrate run-fail tests in src/test/ui from error-pattern to check-run-results

[tmiasko]

As tests are moved from src/test/run-fail to src/test/ui #65440 the meaning
of // error-pattern in ui tests becomes overloaded , since tests in
src/test/run-fail match error patterns to executable output while
src/test/ui tests match them to compiler output.

The changes in #65759 enable such overloaded use: if test is expected to
compile successfully and will be run, the patterns are matched to executable
output, otherwise patterns are matched to the compiler output.

@petrochenkov suggested that it might be preferable to migrate those test to use check-run-result instead.

1. Decide if check-run-result is preferable over error-pattern for run-fail tests in ui.
2. Migrate run fail tests to use check-run-result.
3. Remove support for overloaded meaning of error-pattern.

[petrochenkov]

Another option is to do "check-run-results" automatically for all run-* tests and create the .run.stderr / .run.stdout files only if the output is not empty.