Animate SplitPlaceholderView when entering split from overview

Bugs tracked in b/181704764

Bug: 181704764
Test: Tested on phone and large screen in multiple orientations

Change-Id: I07509006ae3d1f4425dc5119d0c8ed52b41a3bc2

src/com/android/launcher3/anim/PendingAnimation.java

@@ -56,6 +56,10 @@ public class PendingAnimation implements PropertySetter {
         mAnim = new AnimatorSet();
     }
 
+    public long getDuration() {
+        return mDuration;
+    }
+
     /**
      * Utility method to sent an interpolator on an animation and add it to the list
      */