feat(jvm_extractor): assign a corpus to compilation units (#5320)

This now uses the same logic as the java extractor:

https://github.com/kythe/kythe/blob/4aff6ac52c27de4d306b73982b343d6dcae4c2a7/kythe/java/com/google/devtools/kythe/extractors/java/JavaCompilationUnitExtractor.java#L297-L313
1 file changed