Obfuscate visibility of notification-related events.

UsageStats will return obfuscated NOTIFICATION_SEEN or
NOTIFICATION_INTERRUPTION events to callers of #queryEvents
and #queryEventsForUser if they don't hold the MANAGE_NOTIFICATIONS
permission.

Additionaly, refactor the query API in UsageStats to take in flags as
defined in UsageEvents to make future obfuscation/visibility parameters
cleaner.

Also, add the MANAGE_NOTIFICATIONS permission to shell for CTS test.

Bug: 144724524
Test: atest android.app.usage.cts.UsageStatsTest
Test: atest com.android.server.people.data.UsageStatsQueryHelperTest
Test: atest android.content.pm.cts.shortcutmanager.ShortcutManagerUsageTest
Change-Id: I118de7e589ac8dd5924d3740c70903fa484b79b5