[NUI] Add VelocityTracker

[JoogabYun]

Description of Change

This is a utility that calculates velocity from consecutive touch coordinates.

Velocity can be calculated using the motion event coordinates of touch or pan gestures.

      private void OnPanGestureDetected(object source, PanGestureDetector.DetectedEventArgs e)
      {
          tracker.AddMovement(e.PanGesture.ScreenPosition, e.PanGesture.Time);
          if (e.PanGesture.State == Gesture.StateType.Started)
          {
          }
          else if (e.PanGesture.State == Gesture.StateType.Continuing)
          {
          }
          else if (e.PanGesture.State == Gesture.StateType.Finished || e.PanGesture.State == Gesture.StateType.Cancelled)
          {
              float panVelocity = (ScrollingDirection == Direction.Horizontal) ? tracker.GetVelocity().X : tracker.GetVelocity().Y;
              tracker.Clear();
          }
      }

You can use the tracker that NUI provides by default, or you can use a customTracker created by the developer.

      // You can use custom trackers created by yourself
      Tizen.NUI.Utility.VelocityTrackerStrategy[] strategy = new CustomVelocityTracker[2];
      for(int i=0 ; i<2; i++)
      {
        strategy[i] = new CustomVelocityTracker();
      }
      customTracker = new Tizen.NUI.Utility.VelocityTracker(strategy);

      // you can use default tracker
      tracker = new Tizen.NUI.Utility.VelocityTracker();
...
 public class CustomVelocityTracker : Tizen.NUI.Utility.VelocityTrackerStrategy
  {
     ...
  }

API Changes

• ACR: