All AppleJack controllers start in mouse emulation mode, behaving exactly like
ADB mice. Only upon receiving a Listen command on register 3 with handler ID
0x46 does the AppleJack switch protocols, albeit such a change consisting merely
of expanding register 0's buffer size to 4 bytes. In this state, the first 2
bytes remain defined as they are for an ADB mouse; the additional 16 bits carry
the respective states of each of the AppleJack controller's remaining 11 buttons
out of a possible supported 16.
For backward compatibility, honor both mouse clicks and shoulder button presses
on the host when considering the state of the emulated trigger buttons.
