new(demo): respect prefersReducedMotion and leverage in happo

[williaster]

This PR adds the following logic discussed in #1030

📝 Documentation

• checks for the prefersReducedMotion media query in the /xychart, /axis, and /patterns demos, and uses animated or unanimated components accordingly (also removes animationTrajectory controls accordingly).

EDIT: even if prefersReducedMotion=true, users can still toggle animation on/off.

🏠 Internal

• sets prefersReducedMotion: true for happo tests, and removes the happo rendering timeouts that were previously needed for animations

Tested the happo examples locally, and tested gallery examples with / without prefersReducedMotion set on my OS.

@lencioni @kristw @hshoff

[coveralls]

Pull Request Test Coverage Report for Build 516451309

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 61.749%

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Totals
Change from base Build 514010163:	0.0%
Covered Lines:	1786
Relevant Lines:	2753

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💛 - Coveralls

[lencioni]

Love it!

[lencioni]

I think it might be nicer to always render these controls, and then just disable them and add a message explaining why so that people who visit this page with prefers reduced motion are still able to see how it can be used. It would be even better if there was a way for these people to override and enable the animations anyway if they want to see the demo with the animations without having to mess with their OS settings or whatever.

[williaster]

good call, I updated the examples to have an enable animation toggle with a default determined by prefersReducedMotion.