Support monitor input per display (2/2)

To support system gesture per display,
monitor Input should be separated by display.
So each DisplayContent would contain its own
PointerEventDispatcher to detect system gesture.

Bug: b/115602714
Test: atest DisplayContentTests ActivityManagerMultiDisplayTests
Test: atest inputflinger_tests
Change-Id: I7889128af82f0d61dbdc89a84d6ccf0b337e38b4