Parallel front end need some tests in CI, to prevent certain changes from making it unavailable. (e.g. #113730)
### Tasks
- [x] Modify compiler test harness to support repeated testing
- [x] Testing with many threads
- [x] use parallel front end in UI tests
- [ ] make the parallel UI tests blocking on CI
Parallel front end need some tests in CI, to prevent certain changes from making it unavailable. (e.g. #113730)