evaluate stepper option to Carousel

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Carousel was converted to use TWIXT/Animation in phetsims/sun#381. The default is stepper: 'manual', which means that the client must call step to control the Carousel's animation. To avoid having to make changes in this sim, stepper: 'timer' was added to Carousel call sites, which means that the animation will run automatically using the sim Timer.

The responsible developer (that would be me) should evaluate what stepper value should be used.

[pixelzoom]

@jonathanolson randomly selected to review.

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Blocked until @samreid changes the default for Animation stepper, as planned in phetsims/twixt#19 (comment).

[samreid]

phetsims/twixt#19 (comment) seems to imply that the Carousel default should also be the PHET_CORE/Timer instead of manual.

[samreid]

I've changed the default for Animation to timer and correspondingly changed the default for Carousel to timer. This means they will automatically run with PHET_CORE/timer instead of requiring manual steps. Even though phetsims/twixt#19 isn't quite closed yet (it is pending testing and review), the bulk of the work is done, and it may be possible to proceed on this issue.

[jonathanolson]

I've changed the default for Animation to timer

That sounds like a large API change, but I see cases (like in AnimationTests) that are manually stepped but use the default still. Are there cases that still need to be updated?

[samreid]

I tried to catch as many cases as I could in the commits listed after phetsims/twixt#19 (comment), but maybe I missed some. I can re-review them. Thanks for pointing out the missed case in AnimationTests. I'll reassign phetsims/twixt#19 to double check.

[pixelzoom]

stepper: timer (the new default for Carousel) is appropriate for function-builder. Closing.