Provide statistics about ignored/accepted files after indexer run

[tulinkry]

It would be nice to have some statistics about ignored/accepted file/dir counts (especially in the light of recent bug in IgnoredNames #1383) as it might provide quick sanity check at the end of indexing.

[vladak]

This should be intelligent w.r.t. indexing done during preparation (#1351) and index phases, e.g. report the ignored counts after each phase.