Add method to retrieve focused display from the Dispatcher

For the input events that do not have atarget display associated them
them dispathcer send them to current focused display.

This CL adds a method to retrieve the focused display via the
PointerChoreographerPolicyInterface. This will be used to dismiss the
mouse pointer on the appropriate display when the user is typing on the
keyboard.

Bug: b/338652288
Test: atest inputflinger_tests
Change-Id: I2fcda1afad4f046d7f3a4fc1c4762ed42aa3e377