docs(arcballcontrols): Add enableFocus (#1387)

Author: kxxhan

types/three/examples/jsm/controls/ArcballControls.d.ts

@@ -69,6 +69,11 @@ declare class ArcballControls extends Controls<ArcballControlsEventMap> {
      */
     enableAnimations: boolean;
 
+    /**
+     * Enable or disable camera focusing on double-tap (or click) operations. Default is true.
+     */
+    enableFocus: boolean;
+
     /**
      * When set to true, a grid will appear when panning operation is being performed (desktop interaction only). Default is false.
      */