UsageStats: Change INTERACTION to SYSTEM_INTERACTION

SYSTEM_INTERACTION events are signals to the system for a package's
implicit actions (service bound, etc).

These should not affect the API visible stats like lastTimeUsed, etc.
USER_INTERACTION is for user initiated actions (notification interaction, etc).

Bug:21761781
Change-Id: I4585cf35fbb158612a3c737710108bec34e89183
11 files changed