Fix confusion of userId vs. uid

Some functions were trying to get the UserHandle of a userId,
but were instead treating the userId as a uid, and thereby
getting the wrong UserHandle.

Bug: 162543841
Test: atest com.android.internal.app.ChooserActivityTest
Test: atest com.android.internal.app.ResolverActivityTest
Test: atest ScreenshotNotificationSmartActionsTest
Test: atest com.android.server.devicepolicy.DevicePolicyManagerTest
Change-Id: Ib977267e3bae0aa3c7b6b31cfe8f0b3f9cc884b1