Docs: Add Block API Version 3

[Soean]

What?

Adds Block API Version 3 to the docs.

• Preview: https://github.com/WordPress/gutenberg/pull/53046/files?short_path=ba3988a#diff-ba3988a382f32fc709344b591307629b502c2d7cf3b58c21d1e1a5d8db69ccd8
• Live Page: https://developer.wordpress.org/block-editor/reference-guides/block-api/block-api-versions/

More about the API Version and iframed editor:
https://make.wordpress.org/core/2023/07/18/miscellaneous-editor-changes-in-wordpress-6-3/
https://make.wordpress.org/core/2021/06/29/blocks-in-an-iframed-template-editor/

[fabiankaegy]

Thank you for adding this :)

I think we should also note that the block editor gets only iframed if all blocks use apiVersion 3 and also no classic meta boxes like for example Yoast SEO are rendered…

That threw me when I ran into this updating all our blocks to get to this state

[Soean]

Thanks for the addition.

shouldIframe={
	( 
		( hasV3BlocksOnly || ( isGutenbergPlugin && isBlockBasedTheme ) ) 
		&& ! hasMetaBoxes 
	) 
	|| isTemplateMode 
	|| deviceType === 'Tablet' 
	|| deviceType === 'Mobile'
}

https://github.com/WordPress/gutenberg/blob/trunk/packages/edit-post/src/components/visual-editor/index.js#L357C7-L364C8

[fabiankaegy]

I left one note on what I think would be a great addition. But approving as is :)

[github-actions]

Flaky tests detected in 68b0601.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/5689009552
📝 Reported issues:

• [Flaky Test] should not allow blocks to be inserted in inner blocks #44341 in specs/editor/plugins/cpt-locking.test.js