Restrict access to instant app data in usage stats

- Events are obfuscated based on whether the app was instant or not at
the time each event was logged.

- UsageStats are obfuscated based on whether each app is instant or
not at the moment.

Bug 38202133
Test: Manual test using UsageStatsTest and instant apps

Change-Id: I3c74309196b88d010d317cb0dd6749bf4624e876