Docs: Add variations key to block.json JSON schema definition

[fabiankaegy]

What?

Add the variations key with all of its available sub properties to the block.json JSON schema.

Why?

The JSON Schemas are great because they greatly improve the Developer Experience of working with custom blocks. However, they aren't of much use if they are not including all the options that are actually available.

Closes #40490.
Part of #41236.

How?

Testing Instructions

will update this once the initial testing passes

[fabiankaegy]

One question I have for this addition is how we handle the actual versioning of this. Technically this is possible in block.json files since WordPress 5.8. So in theory it would need to get merged into the wp/5.8, wp/5.9, and wp/6.0 branches.

[gziolo]

One question I have for this addition is how we handle the actual versioning of this. Technically this is possible in block.json files since WordPress 5.8. So in theory it would need to get merged into the wp/5.8, wp/5.9, and wp/6.0 branches.

Was it WP 5.8 when it got introduced? It would make perfect sense to cherry-pick this commit tho all those branches then 👍🏻

We also miss the section for variations on the Block Metadata reference page:

https://github.com/WordPress/gutenberg/blob/trunk/docs/reference-guides/block-api/block-metadata.md#block-api

It doesn't need to be so detailed as we can always reference another page:
https://github.com/WordPress/gutenberg/blob/trunk/docs/reference-guides/block-api/block-variations.md

The only remark would be that JavaScript functions (isActive) and React elements (icon) can't be used in block.json.

[fabiankaegy]

@gziolo I added Variations to the block metadata documentation and included the callout you've mentioned 👍

[fabiankaegy]

Also @gziolo I just checked in Core and it looks like it was introduced in 5.9 WordPress/wordpress-develop@d9599ad

So we should only cherry-pick it on the wp/5.9 and wp/6.0 branches

[gziolo]

Excellent job documenting block variations with block.json ❤️

I left some nitpicks to polish just before landing this PR. Thank you so much for the initiative!

[gziolo]

Also @gziolo I just checked in Core and it looks like it was introduced in 5.9 WordPress/wordpress-develop@d9599ad

So we should only cherry-pick it on the wp/5.9 and wp/6.0 branches

Awesome, good job checking it 👍🏻

[fabiankaegy]

@gziolo Added two new PR's to backport the changes to the release branches here:

• Backport: Add variations key to block.json JSON schema definition to wp/5.9 #42552
• Backport: Add variations key to block.json JSON schema definition to wp/6.0 #42553