feat: add SpringContext component

[aleclarson]

🚀 Feature Proposal

Add a SpringContext component that can pause, cancel, or finish any animation within its child components.

// Every react-spring animation inside "Home" is affected.
const App = () => (
	<SpringContext pause={true} cancel={true} immediate={true}>
		<Home />
	</SpringContext>
)

You can nest SpringContext components to override props for a subtree.

Motivation

Provide an easy way to reduce CPU cycles by pausing animations when they're not visible.

[aleclarson]

The immediate prop works well with #811 (comment)

[ShanonJackson]

Don't feel like this is neccessary; you can already achieve this yourself through providing your own context + listening for that context in component's that useSpring and setting immediate/cancel/paused etc.

If you want it natively (I.E Inbuilt context listeners) then just extend animated.div yourself