WindowManager: Support focus for SurfacePackage overlays

We already support granting focus to SurfaceControlViewHost
embedded windows. In the normal path where the SurfacePackage
is embedded in a client view hierarchy, we rely on the client
to invoke grantEmbeddedWindowFocus(true/false) as the SurfaceView
hosting the SurfacePackage moves in and out of focus according
to client side state. For server hosted overlays, we can reuse
grantEmbeddedWindowFocus but we need someone to call it. To accomplish
this we reorganize the logic in handlePointerDownOutsideFocus to
work in terms of InputTarget instead of WindowState, and graft in
the appropriate logic for EmbeddedWindows inside
EmbeddedWindowController.java.

Bug: 214239638
Test: Existing tests pass
Change-Id: Ie91b8cf790b4ab2092a90e310e7bd200a4adcff4