Permission enforcement for A11y volume changes

Make modifying the STREAM_ACCESSIBILITY volume conditional
  to have the BIND_ACCESSIBILITY_SERVICE permission.
Add BIND_ACCESSIBILITY_SERVICE permission to sysUI.

Test: cts-tradefed run cts -m CtsMediaTestCases -t android.media.cts.AudioManagerTest#testAccessibilityVolume
Bug: 34379420
Bug: 30448020
Change-Id: I9f26affccd953bd8473d06822857edf92fef4ba8