feat(skeleton): add skeleton component

[dancormier]

STACKS-752

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This PR adds a Skeleton component with a base monochromatic style and an ai variant.

cc @kylejrp

Details

Stacks Svelte implementation

Previously, a version of this component was maintained solely in our Stacks-Svelte library 🔒, but we've had requests for modification that made this seem like a good time to lift it into Stacks Classic. I've created a companion Stacks-Svelte PR 🔒 to support these changes.

Screenshots

Light mode

Dark mode

Light high contrast mode

Dark high contrast mode

How to test

• Run this PR locally and visit the Skeleton docs page (or check out the deploy preview)
• Verify that it renders and is styled as expected
• Bonus: Verify the appearance in dark and HC modes

For design

• Please verify the value choices for the base style. This style is new and I used my best judgement for the values. FWIW, the AI variant should look identical to the style currently set as the base style for the Stacks-Svelte Skeleton component.

[changeset-bot]

🦋 Changeset detected

Latest commit: 25cc9d1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@stackoverflow/stacks	Minor

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[giamir]

Great work @dancormier. Thanks for porting this over to Stacks Classic. It looks very good to me, including docs and tests. 🎉
After design gives the thumbs up I would be happy to see this merged.