SyncPointerCapture (3/n): Add Capture event to InputChannel

This CL adds the ability to send a CAPTURE event through the
InputChannel, and adds the appropriate processing logic to
InputPublisher and InputConsumer.

This will be used by the InputDispatcher to notify windows when they
have either lost or gained Pointer Capture.

Bug: 141749603
Test: atest libinput_tests
Change-Id: I102833e6f0fd1e8e9c4b3c12e7a5a737eeda2377