Add multi-display support

This change modifies and implements below methods to support
multi-display device implementations.
- getIGraphicBufferProducer() takes a target display identifier.
  If a given identifier is not valid, this will return a null pointer.
- AutomotiveDisplayProxyService stores display tokens of each display.
- showWindow() is modified to set a layer stack properly for a target
  display.
- getDisplayIdList() is newly implemented and returns stable IDs
  of all available displays.
- getDisplayInfo() returns the description of a target display
  that is identified by a given stable ID.

Bug: 141886260
Bug: 146567078
Test: VtsHalEvsV1_1TargetTest
Change-Id: Ia195a6c19416eb75bfe77da61d7a32030ec85967
Signed-off-by: Changyeon Jo <changyeon@google.com>