Plumb FocusChanged events to CarService

To implement Driver performance isolation, we need a signal to notify
that the top focused display is changed.
WindowChangeListener#focusChanged() can provide it, but it's hidden api.
So, we register it in CSHS and plum it to  CarService.

Bug: 300502877
Test: TBD
Change-Id: Icb4d3089714d801738054388f1fa6ca408fb0fb3
6 files changed
tree: 1c2aca46b86ef44acee05ca0491bdf47034a3e2a
  1. builtInServices/
  2. tools/
  3. updatableServices/
  4. .gitignore
  5. OWNERS
  6. PREUPLOAD.cfg