[Feat]: Rename snap index options and methods to achieve consistent naming

[davidjerleke]

Which variants of Embla Carousel are relevant to this feature request?

• embla-carousel (Core)
• embla-carousel-react
• embla-carousel-vue
• embla-carousel-svelte
• embla-carousel-autoplay
• embla-carousel-auto-scroll
• embla-carousel-solid
• embla-carousel-auto-height
• embla-carousel-class-names
• embla-carousel-fade
• embla-carousel-docs (Documentation)
• embla-carousel-docs (Generator)

Feature description

All options and methods about snaps should be renamed to achieve more consistent naming:

• selectedScrollSnap --> selectedSnap
• previousScrollSnap --> previousSnap
• startIndex --> startSnap
• scrollSnapList --> snapList

Additional Context

• PR: [Feat]: Rename snap index options and methods to achieve consistent naming #1090.

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