Make UsageStats query API UserHandle-aware

Allow queryUsageStats to take in the context's userId. This
allows apps like Settings to query usage stats across
profiles.

Bug: 146921442
Test: atest CtsUsageStatsTestCases:UsageStatsTests
Change-Id: Ia6c90c1a31887efa8d5446c1b1b11e75cb9ab83e