Fix: Decay (a.k.a intertia) with immediate

[joshuaellis]

Why

This PR should resolve #1026 & because it's bugging me at the same time it should resolve #1437

What

If an animation has immediate set and that value changes it does not look to "start" the animation at all, it will if you change a value such as decay so the following code would work:

if(down)}{
 api.start({ pos, immediate: true })
}
else {
 api.start({ pos, config: { velocity: 2, decay: true } })
}

but in reality this is cumbersome and the following should work:

api.start({
 pos,
 immediate: down,
 config: { velocity 2, decay: true }
})

Which it now does.

Checklist

• Documentation updated
• Demo added
• Ready to be merged

[codesandbox-ci]

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Latest deployment of this branch, based on commit 082aae4:

Sandbox	Source
spring-card	Configuration
spring-goo-blobs	Configuration
spring-flip-card	Configuration
spring-slide	Configuration
spring-draggable-list	Configuration
spring-cards-stack	Configuration
spring-viewpager	Configuration
spring-simple-transition	Configuration
spring-image-fade	Configuration
spring-list-reordering	Configuration
react-spring touch scrolling example	Issue #1026
Decay - V9.0.1 Jump	Issue #1437
Decay - V9.0.1 Jump	Issue #1437

[HQ92]

Looking forward to this fix as I think it's the last piece of the puzzle to making natural feeling touch friendly draggable sliders with real physics based animations without any weird jumping! Looking forward to testing it out.

You can see the issue in my draggable slider currently at https://codesandbox.io/s/react-spring-912-inertial-spring-kyq3d?file=/src/index.js, I'm happy to test once it's been pushed.