Change default interpolation of TimingTransition to AccelerateDecelerate

Summary: LinearInterpolation doesn't produce natural curve that occur in real world where you'd expect easing in and out when moving items. Moreover, default interpolator in Android animations is also non-linear interpolator. Switching default of Timing animator to AccelerateDecelerateInterpolator like in default android animations.

Reviewed By: astreet

Differential Revision: D8478562

fbshipit-source-id: 91f421a0da626bd4391848bf1515296fcc201580

litho-core/src/main/java/com/facebook/litho/Transition.java

@@ -15,6 +15,7 @@
  */
 package com.facebook.litho;
 
+import android.view.animation.AccelerateDecelerateInterpolator;
 import android.view.animation.Interpolator;
 import com.facebook.infer.annotation.ThreadSafe;
 import com.facebook.litho.animation.AnimatedProperties;
@@ -516,12 +517,14 @@ public TransitionAnimationBinding createAnimation(PropertyAnimation propertyAnim
    */
   public static class TimingTransitionAnimator implements Transition.TransitionAnimator {
 
+    private static final Interpolator DEFAULT_INTERPOLATOR = new AccelerateDecelerateInterpolator();
+
     final int mDurationMs;
     final Interpolator mInterpolator;
 
-    /** Create timing animator with linear interpolation. */
+    /** Create timing animator with accelerate decelerate interpolation. */
     public TimingTransitionAnimator(int durationMs) {
-      this(durationMs, null);
+      this(durationMs, DEFAULT_INTERPOLATOR);
     }
 
     /** Create timing animator with custom Android interpolator. */