VolumeZen: Introduce internal vs external ringer mode.

Stabilize mapping between ringer-mode=silent and zen=priority
by keeping track of two ringer modes:
 - Internal ringer mode: Used for underlying stream muting
 - External ringer mode: Reported to clients

The mapping between external ringer mode + zen is:
 - normal = all
 - vibrate = all
 - silent = priority (read-write) or none (read)

Changes include:
 - Remove "zen check" from audio service, back to audio
   service having no knowledge of zen.
 - Maintain a new external ringer mode in audio service,
   this is the ringer mode reported through AudioManager
   to callers, also mapped to the change intent.
 - Introduce a "ringer mode delegate" to the local
   audio manager interface, responsible for observing
   external / internal mode changes, and making changes
   if necessary.
 - Internal ringer mode changes are still interesting
   to the volume dialog, wire up a callback through
   the existing IVolumeController interface.
 - On devices without vibration, the mapping is the same
   but since no ringer mode change is possible, disable
   the icon toggle and remove the mute icon when volume=0.
 - On devices with vibration, volume down presses should
   pulse the vibrate icon (and vibrate) as a hint that this
   is as low as the device can go using the keys.  Since
   the mechanics are similar to the existing zen=none hint,
   pull into shared helper.
 - Log ringer mode changes to the zen log, include calling
   package information for issue diagnosis.
 - Include whether vibration is supported in the audio service
   dump.
 - Update the status bar icon policy to use the internal ringer
   mode, not the external mode (for vibrate icon).
 - Update the "Muted by <x>" logic, include current suppressor
   in dumpsys, ensure suppression icon is enabled & !clickable,
   regardless of zen mode.

Bug: 17884168
Bug: 15471679
Bug: 16824970
Change-Id: Ia7d3bb23ce6d1e37b24fb6521d1c1ab9bb8f60c0