[NUI] Fix LottieAnimationView not to reference disposed delegate

[NUI] Fix LottieAnimationView not to reference disposed delegate

Delegate rootCallback of LottieAnimationView is called by multi threads
for lottie dynamic properties.

This causes the following issues.
- Delegate rootCallback of disposed LottieAnimationView can be
  referenced.
- Local variables in RootCallback is disposed by multi threads.

To resolve the above issues, the followings are done.
- Delegate rootCallback of LottieAnimationView is changed to be static.
- Local variables in RootCallback is not disposed.