Move non-state methods into MouseService

Fixes #5756

src/browser/TestUtils.test.ts

@@ -393,9 +393,8 @@ export class MockMouseService implements IMouseService {
     throw new Error('Not implemented');
   }
 
-  public bindMouse(): void {
-    throw new Error('Not implemented');
-  }
+  public bindMouse(): void { }
+  public reset(): void { }
 }
 
 export class MockRenderService implements IRenderService {