Add option to retrieve pending intent result

Used by SystemUI to check whether an activity start will
actually lead to something animating.

Also fixes an issue where we return MOVED_TO_FRONT instead of
DELIVERED_TO_TOP.

Test: go/wm-smoke
Test: Use PendingIntent.sendAndReturnResult
Change-Id: I2b6bfca0a53125635bc462f32ab7eaae366c0c8a