[feature-request] Support dynamic spring, initial delay features. #3

1. Feature description

1. Support dynamic state-preserved spring TimingFunction for reactive animation.
2. Support initial animation delay feature that can be positive and negative.

2. Changes

• Add a.timing.dynamicSpring
• Add timeline.play({..., delay: 50 // 50ms })

3. Breaking change (y/n):

n

4. Additional Information(context, links, etc.)

n