Use the last cooked touch state for generating button release events

This bug was exposed by the refactor in ag/20068126 that cleans up the
CookedPointerState by ensuring it is always zero-initialized.

Button release events are generated before the touch state change events
are generated. If the touch goes up before or at the same time as the
button goes up, the "current" touch state will have no pointers.

The old logic got around this by using the getting the values for the
"last" touch state's pointers from the "current" touch state. This
wrong, because the "last" state's pointers no longer exist in the
"current" state. However, because the CookedState copying logic
never reset the underlying PointerCoords data after the pointer is
lifted, the "last" state's pointer's values were essentially preserved
in the "current" state in some cases. This meant the expected behavior
was observed most of the time even though the logic was incorrect.

This CL corrects the button release event generation logic to ensure
that "last" state is used when generating those events.

Bug: 245989146
Test: atest inputflinger_tests
Change-Id: I9889e7f816f4ba885eae783ebf4c7721eb60db3a