Core: separately log file deletions

Today you can turn on lucene.iw's TRACE logging, but that gives you a metric ***load of output.

This change breaks out lucene.iw.ifd separately (TRACE), and also index.store.deletes.

The logging is unfortunately redundant, meaning if Lucene deletes a file, you'll see log output from both lucene.iw.ifd and in index.store.deletes; I did this so that if something else (not Lucene) deletes a file through the Store.directory(), we'd see it logged as well.

I found only 2 places in ES that seem to be deleting files associated with a Lucene index, and I added logging there as well.

Unfortunately, these produce a lot of output ... so I did not turn them on by default.

Closes #8603