Move toggle voice access shortcut to accessibility category

Update KEY_GESTURE_TYPE_TOGGLE_VOICE_ACCESS to be in
accessibility category since the new category was created in
Ia6a52a518c9382126e2f3e522a9d37f8139b4414

Screenshot:
  1. The shortcuts showing up in the accessibility tab:
    go/screenshot-7agliczshjvrwuk
  2. The shortcuts being customized successfully:
    go/screenshot-4ckwearvajjtyqd

Bug: 389652455
Test: verified locally
Flag: com.android.hardware.input.enable_voice_access_key_gestures
Change-Id: I74e6f227119e94fe3e515843d2695e7224ab0014