Convert gesture navigation tutorial still image vector drawables to layout files

Bug: 192939067
Test: manual, started full tutorial, started home, back and overview individually, locked and unlocked phone mid-tutorial step.
Change-Id: I1cba811c556139bc9ba52459f1b27f21eb156ac0

quickstep/src/com/android/quickstep/interaction/HomeGestureTutorialController.java

@@ -42,8 +42,8 @@ final class HomeGestureTutorialController extends SwipeUpGestureTutorialControll
     }
 
     @Override
-    protected int getMockAppTaskThumbnailResId(boolean forDarkMode) {
-        return forDarkMode ? R.drawable.mock_webpage_dark_mode : R.drawable.mock_webpage_light_mode;
+    protected int getMockAppTaskLayoutResId() {
+        return R.layout.gesture_tutorial_mock_webpage;
     }
 
     @Override