Fix hold volume keys don't trigger the one handed mode in

One-handed mode settings page

Add to support observing A11y's Shortcut Hardware provider key
ACCESSIBILITY_SHORTCUT_TARGET_SERVICE

Bug: 193411296

Test: manual verified on System > Gestures > One-handed mode shortcut

Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures
      .OneHandedEnablePreferenceControllerTest"
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures
      .OneHandedMainSwitchPreferenceControllerTest"
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures
      .OneHandedActionPullDownPrefControllerTest"
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures
      .OneHandedActionShowNotificationPrefControllerTest"
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
"com.android.settings.gestures
.OneHandedPreferenceCategoryControllerTest"

Change-Id: I4704a56873f14e52db8f7c0468eed17f190c5dce