Usagestats dumpsys print list of usagestats database files.

Print total number and list of daily/weekly/monthly/yearly files, so
we can tell if excessive number of files are created.

Bug: 125426689
Test: "adb shell dumpsys usagestats" and search for UsageStatsDatabase
Change-Id: Id5c6028151d4c21e019820f7b6070712283f4983