Fix all apps tab fling detection

It is a regression when we changed from ViewPager to PagedView.
Unlike ViewPager, PagedView does not take "yDiff" into account
when determining should it intercept its child MotionEvent.

Override determineScrollingStart, just like what we did in Workspace

Change-Id: I25f7415c45c370629558d944f59bf95c741b9319
FIX: 73878167

src/com/android/launcher3/PagedView.java

@@ -1892,6 +1892,14 @@ public abstract class PagedView<T extends View & PageIndicator> extends ViewGrou
                 getNextPage() + 1, getChildCount());
     }
 
+    protected float getDownMotionX() {
+        return mDownMotionX;
+    }
+
+    protected float getDownMotionY() {
+        return mDownMotionY;
+    }
+
     @Override
     public boolean onHoverEvent(android.view.MotionEvent event) {
         return true;