fix(RenderWindowInteractor): guard against undefined exitPointerLock

Certain versions of Safari on iOS do not implement document.exitPointerLock.

Author: floryst

Sources/Rendering/Core/RenderWindowInteractor/index.js

@@ -430,7 +430,7 @@ function vtkRenderWindowInteractor(publicAPI, model) {
   };
 
   //----------------------------------------------------------------------
-  publicAPI.exitPointerLock = () => document.exitPointerLock();
+  publicAPI.exitPointerLock = () => document.exitPointerLock?.();
 
   //----------------------------------------------------------------------
   publicAPI.isPointerLocked = () =>