Add ACTION_CANCEL to input command

To test various cancel scenarios, add ACTION_CANCEL support to input
command.

Test: adb shell input motionevent DOWN 500 500 && adb shell input
motionevent CANCEL 500 500
Test: on cuttlefish:
$ adb shell input motionevent DOWN 0 0
$ adb shell input motionevent MOVE 100 100
$ adb shell input motionevent CANCEL
$ adb shell input motionevent CANCEL 100 100
Bug: 155362798

Change-Id: I01a7f6e4d0575856fd649e8f55efeb620006fff8