New Settings preference for One Handed mode

Add toggles in Settings location:
Settings > System > Gesture > One-Handed

Bug: 151130376

Test: manual check Settings > System > Gesture > One-Handed
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures.OneHandedSettingsTest"
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures
      .OneHandedAppTapsExitPreferenceControllerTest"
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures
      .OneHandedEnablePreferenceControllerTest"
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures
      .OneHandedTimeoutPreferenceControllerTest"
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures.OneHandedSettingsUtilsTest"

Change-Id: Iafbd3ad051ff0f9c2f4a1b6fcacdccc137b65d0c