Support for user preferences like prefers-reduced-motion and prefers-color-scheme

[AlaricBaraou]

Expose the two preference through a context provider to all childrens.

To test it, refer to your OS settings.

I'll update the demo to prevent all animation if prefers-reduced-motion = reduce and enable / disable dark theme based on prefers-color-scheme: dark

If a change is made in the preference while visiting the page, the provider / app will update in consequence.

The idea came from this tweet : https://twitter.com/ericwbailey/status/1351243179060768778

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size-limit report 📦

Path	Size
dist/a11y.cjs.production.min.js	3.32 KB (+6.5% 🔺)
dist/a11y.esm.js	3.2 KB (+7.39% 🔺)

[AlaricBaraou]

The context is not passed through the r3f canvas. If we need to access it outside and inside of it it's not convenient.
I'll give it a thought before merging.
Otherwise it works well and the demo have been adapted to showcase it.