Fix FollowMeToggle's auto-follow breaking if the component is disabled (#10620)

* Fix FollowMeToggle's auto-follow breaking if the component is ever disabled

`FollowMeToggle` has an `AutoFollowAtDistance` feature which breaks if the `FollowMeToggle` component is ever disabled and re-enabled. This is because the `AutoFollowAtDistance` property setter checks if the `autoFollowDistanceCheck` coroutine is null before starting the coroutine. If the component is disabled, the coroutine will _stop_ but not become null. When the component is re-enabled, the coroutine does not start again because the previous instance is non-null, even though it is no longer running.

This is fixed by simply setting `autoFollowDistanceCheck` to null in `OnDisable()`.

* FollowMeToggle: formatting tweak

Per keveleigh

Co-authored-by: Kurtis <[email protected]>

Co-authored-by: Kurtis <[email protected]>

Author: kevinfoley

Assets/MRTK/SDK/Features/UX/Scripts/Slate/FollowMeToggle.cs

@@ -183,6 +183,11 @@ private void OnEnable()
             // Begin the follow coroutine when enabled.
             AutoFollowAtDistance = autoFollowAtDistance;
         }
+        
+        private void OnDisable()
+        {
+            autoFollowDistanceCheck = null;
+        }
 
         #endregion MonoBehaviour Implementation