Add accessibility shortcuts to shortcut helper

Add the following shortcuts to shortcut helper:
 - KEY_GESTURE_TYPE_TOGGLE_BOUNCE_KEYS
 - KEY_GESTURE_TYPE_TOGGLE_MOUSE_KEYS
 - KEY_GESTURE_TYPE_TOGGLE_STICKY_KEYS
 - KEY_GESTURE_TYPE_TOGGLE_SLOW_KEYS

Screenshot:
  1. The shortcuts showing up in the accessibility tab:
     go/screenshot-5x63rst2rehphkb
  2. The shortcuts being customized successfully:
     go/screenshot-9kmow2a5yb8x3pz

Bug: 389652455
Test: verified locally
Flag: com.android.hardware.input.keyboard_a11y_shortcut_control
Change-Id: If1c6df61c6a8f86ec1b01cbe44ad938cfc0048cb