testrunner: fold PreprocessorHelper into TestPreprocessor
#19308
| Job | Run time |
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| 2m 0s | |
| 20s | |
| 8s | |
| 32s | |
| 1m 22s | |
| 1m 22s | |
| 1m 18s | |
| 1m 10s | |
| 3m 19s | |
| 1m 19s | |
| 1m 29s | |
| 1m 30s | |
| 15m 49s |