Adds a code when statsd sends intent to getData.

If the data receiver is experiencing delays, there may be a queue of
multiple intents to collect the same data. This timestamp makes it
easy in the receiver to de-dupe these requests to call getData.

Also, we update how StatsCompanionService gets the snapshot by
requesting data for all known apps. I notice that Keep seems to have
a uid active even when it appears uninstalled.

Bug: 77981668
Test: Flashed marlin-eng and manually verified.
Change-Id: I509e19383ec4a5da8746dd0c76ac71a948c6877d