Volume: Delay adjustments made when showing ringer UI.

Since the volume rocker is now the primary system UI for
entering ringer modes, we need to provide a way to display
the ui without making a sound.

Change the policy for the ringer stream to only display the
UI on the initial adjustment request, don't actually make
an adjustment.  However, don't break previous ability to
press and hold the vol keys down to vibrate, so allow this
after the standard framework long-press delay.

Audio service had no way of knowing whether or not the registered
volume controller was visible, so add a mechanism for the
controller (volume panel) to send that info back to the service.

Found and fixed a discrepancy between AudioManager.handleKeyDown
and MediaSessionLegacyHelper so that an adjustment over the
keyguard is allowed to vibrate as well as play sound during
adjustments.

Bug:16202639
Change-Id: Icd36c23e8d08c4ed57922c05724b281f32049be7