Fix overshoot velocity in 2-button landscape mode

Now we use the velocity towards the middle of the screen
(e.g. x when in landscape) instead of always using y.

Test: testBackground with @PortraitLandscape

Bug: 135567630
Change-Id: I77ab6bdf0d556475a6c182ae91914a718a81e1c4

quickstep/tests/src/com/android/quickstep/TaplTestsQuickstep.java

@@ -17,7 +17,6 @@
 package com.android.quickstep;
 
 import static com.android.launcher3.ui.TaplTestsLauncher3.getAppPackageName;
-
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
@@ -208,7 +207,7 @@ public class TaplTestsQuickstep extends AbstractQuickStepTest {
 
     @Test
     @NavigationModeSwitch
-//    @PortraitLandscape
+    @PortraitLandscape
     public void testBackground() throws Exception {
         startAppFast(resolveSystemApp(Intent.CATEGORY_APP_CALCULATOR));
         final Background background = mLauncher.getBackground();