Add 'Reach to check' to lock screen settings

Also added to Gestures page to make sure we're following the
same structure for all gestures.

Change-Id: Iaa9e53e870165801decfa427441d01ee69bcce6d
Note: using dummy video. dependency on b/112442049
Bug: 111414690
Test: make RunSettingsRoboTests ROBOTEST_FILTER=ReachGesturePreferenceControllerTest
Test: make RunSettingsRoboTests ROBOTEST_FILTER=ReachGestureSettings