Add support for explicit control over model animations #9339

Cesium currently only supports time based animation. This can be inconvenient if the phase of the animation is related to something other than time (eg distance along a path of an object moving at a variable speed). This came up before in CesiumGS#7361, but the author was persuaded that it was better to use nodeTransformations to explicitly control the model. That was (just) doable with that example, because there were just 3 pairs of wheels, all of which needed the exact same, relatively trivial, transformations. The proposed solution was also cumbersome, relying on modifying `multiplier` on the fly, with the downside that modifying multiplier also reset the phase of the animation. For more complex models, with less uniform animations, this approach isn't really doable - especially if you want the same code to work for multiple models. This adds an animationTime function to ModelAnimation. If set, it's used by ModelAnimationCollection.update to compute the localAnimationTime, rather than using the current clock time. I also added an animateWhilePaused property to ModelAnimationCollection. When false (the default), we continue to do the short circuit exit from ModelAnimationCollection.update when the scene time hasn't changed. When true, a suitable animationTime function can continue to animate the model, even when scene time is paused. The new sandcastle example is just a clone of Time Dynamic Wheels, rewritten to use Cesium_Man.glb, and the new functionality.

- rename _prevAnimationTime to _prevAnimationDelta - rewrite the _prevAnimationDelta bailout - add a test that we animate while paused if animateWhilePaused is true, and update the existing test to check that we don't animate while paused when animateWhilePaused is false

Use `defined(scheduledAnimation.animationTime)`

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Add support for explicit control over model animations #9339

Add support for explicit control over model animations #9339

Commits on May 10, 2022