Use fling animation utils for snapChild

Test: manual - swipe open and close the menu beneath the notification shade
      ensure the motion follows finger
Bug: 124097982

Change-Id: I446932d52ccd0d0055d0e37641d9c40c1bd61bd2

packages/SystemUI/src/com/android/systemui/SwipeHelper.java

@@ -474,8 +474,6 @@ public class SwipeHelper implements Gefingerpoken {
         if (anim == null) {
             return;
         }
-        int duration = SNAP_ANIM_LEN;
-        anim.setDuration(duration);
         anim.addListener(new AnimatorListenerAdapter() {
             boolean wasCancelled = false;
 
@@ -495,6 +493,9 @@ public class SwipeHelper implements Gefingerpoken {
         });
         prepareSnapBackAnimation(animView, anim);
         mSnappingChild = true;
+        float maxDistance = Math.abs(targetLeft - getTranslation(animView));
+        mFlingAnimationUtils.apply(anim, getTranslation(animView), targetLeft, velocity,
+                maxDistance);
         anim.start();
     }