Share style environment subscriptions

[ixf]

This reduces RSD's memory overhead in React Native. Measured with https://github.com/ixf/rsd-bench - exact numbers in the readme there

• combine dimensions, color scheme and reduced motion into one store - StyleEnvironmentStore, which replaces PrefersReducedMotionStore - no need to keep two stores around, and wrapping dimensions and color scheme hooks into them reduces number of subscriptions per useStyleProps call
• remove useMemo from useCustomProperties. It has two call sites and the useMemo was useless in both cases