Fixed semanticdb file copying issue, added more tests

[lefou]

Added incremental test for JavaModule.semanticDbData and ScalaModule.semanticDbData. Looks like zinc isn't compiling incrementally at all when we stop at an early compiler phase. The test don't really catch that, yet. But I also found a bug where we moved files instead of copying them.

Fix #3077

[lefou]

Looks like in all test cases zinc is never compiling incrementally. More work is needed. Could be related to the fact that we stop after an early compiler phase.

[lefou]

Here are some issues I identified with our current approach to generate semanticdb data in a Scala 2.13 module:

• When we stop scalac after phase semanticdb-typer, zinc is not able to incrementally compile the next round, therefore we currently always generate all semanticdb files in each run
• If we don't stop scalac after phase semanticdb-typer, we can generate semanticdb data incrementally, but we also unnecessarily compile all scala files to class files
• Incremental compilation doesn't seem to clean semanticdb files for removed sources. So, we need to manually remove those that belong to non-existing source files