Fix VDM UID tracking.

Current problems:
 - Only a single display per device is tracked at a time. If a
   virtual device has more than one display, any listeners will receive
   wrong UIDs
 - UIDs not updated when a display/device is removed. The mapping is
   never updated in that case and any UIDs will forever be considered
   as running on a virtual device
 - AudioController is device-level but tracks only a single display at
   a time as well. Starting a new audio session/device will lose track
   of all UIDs on the previously tracked display.
 - Overall, the UID tracking has an implicit assumption that a virtual
   device can only ever have a single display.

Changes:
 - Remove the GWPC-level listeners. VirtualDeviceImpl now processes all
   UIDs coming from each display's GWPC
 - Combine all display UIDs into device-level UIDs and pass that to all
   relevant clients (AudioController, CameraAccessController, VDMS).
   All they ever care about is the set of all UIDs on a device, they
   do not need display level granularity
 - Notify about empty UID set whenever a display is removed
 - VDMS simply dispatches the new UIDs to any system listeners that are
   registered with VDMInternal
 - Change the VDMInternal listener to take set of UIDs per device,
   instead of all UIDs running on ANY virtual device
 - Simplify the single VDMInternal listener use case (A11y Proxy)
 - Clean up redudndant VDMInternal methods and move the listeners from
   the LocalService to VDMS top level

Implications:
 - Fixing A11yProxy issues with re-launching apps on a new display or
   device after the old one was closed. The A11yProxy is now notified
   about the changes.
 - Fix issues with the AudioController, which will now track all UIDs
   running on the device, regardless of the display.

Bug: 440355882
Bug: 440353845
Fix: 428281968
Flag: EXEMPT bugfix
Test: atest & manual
Change-Id: I27cdea489eefddeb8238d61bcd0d40a8f742befe