Add parallel front-end test set to compiler-test #118698
Description
Parallel front end need some tests in CI, to prevent certain changes from making it unavailable. (e.g. #113730)
### Tasks
- [ ] Modify compiler test harness to support repeated testing
- [ ] Testing with many threads
- [ ] use parallel front end in UI tests
- [ ] support perf test of parallel front end in rustc-perf