✨ [bento][amp-sidebar] Update animations to obey APIs mid-animation

[krdwan]

Sidebar tracker: #31366

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open, close, toggle should update / reverse animations mid-animation

Prior to this change, if close was called while the sidebar was animating open, it would snap to a fully opened state and begin closing. Now, it will begin animating closed from whatever position it was in (so it will reverse from the current position). This can be done multiple times in a single animation by repeatedly calling close, open, close, ... or toggle, toggle, toggle....

Works in both directions: opening and closing.

How it works:

1. Tracks the animation object (in a state variable) while animating and calls reverse() on it when the sidebar is told to animate in a different direction.

to do:

• update tests (animation tests will need to be updated)

[caroqliu]

Had a few questions