Use input token in PointerCaptureRequest

Instead of sending boolean to indicate the capture state,
InputDispatcher now sends an input window token that requests a
pointer capture, or nullptr otherwise.

This is useful for some InputReader implementations.
Also, this token can be used to verify if a pointer capture changed
event from a reader is valid.

Bug: 259346762
Bug: 301628662
Test: inputflinger_tests
Test: android.view.cts.PointerCaptureTest WindowFocusTests#testPointerCapture
Change-Id: Ie8343db6744dc2080f7f1dcff5a630be5c87fa3e