fix(parallax): child horizontal prop defaults to parent's

[kindoflew]

Why

Currently, when Parallax has horizontal={true}, all ParallaxLayers still translate vertically unless horizontal={true} is manually set on all of them. This change makes it so ParallaxLayers' default horizontal matches Parallax's.

What

• Added horizontal to IParallax interface and Parallax's state
• Added a check in ParallaxLayer to see if horizontal === undefined and reassign it if it is.
• Removed a CSS rule in sandbox demo that was causing numbers to appear too far to the left.

Checklist

• Documentation updated: (Pending this being merged)
• Demo added: n/a
• Ready to be merged

You can test this by looking at the sandbox demo "Parallax" (not vert). Currently, when you scroll horizontally, the layers still translate vertically.

This might be a breaking change if anyone is relying on this behavior, but it wouldn't affect anyone who has already manually set horizontal on ParallaxLayers.

I will also submit a PR for the docs to add horizontal to ParallaxLayer's prop list, but will wait until a decision is reached on this so I can accurately describe its behavior. I understand everyone is probably busy with v9 bug fixes, so if this is not a high priority right now, I'll just update the docs to reflect how it currently works.

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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

[kindoflew]

I decided reassigning a prop was probably a smell, so I refactored it to be a new const that replaces horizontal conditionals in ParallaxLayer. All other changes are the same.

[joshuaellis]

Thanks for the contribution!! ⭐ I had thought the demo looked odd when I added it...

[joshuaellis]

Regarding your PR notes, i think this makes perfect sense imo, as long as we clearly state this is in the docs it'll be fine, i'll also update the changelogs to reflect this POTENTIALLY_BREAKING_CHANGE.