App Time Limits API in UsageStats

Allow setting groups of apps to control usage time limits on.
Applies only to activity time in the foreground.

Updated UsageStatsTest app to be able to add an observer for
a 30 second timeout across multiple comma separated package
names.

Bug: 74335821
Test: atest FrameworksServicesTests:AppTimeLimitControllerTests
      Install and run frameworks/base/tests/UsageStatsTest

Change-Id: I677c30b4f211f7acf72c9766df3d8c1ac56a4b4e