Moar Content capture improvements:

- Drop Content Capture events when the session is disabled, otherwise sessions
  on this state might never finish.
- Fixed PII leak.
- Created helper class for common stuff.
- Improved logging.

Test: manually chenged VERBOSE to true, restarted system_server, and watched logcat - without
      this change, launcher's session would never die because it kept re-scheduling flush
      requests.
Test: atest CtsContentCaptureServiceTestCases
Bug: 122959591

Change-Id: Idcc1bbb12763d1cf98149164c68c2712834d5112