Add layout block supports

[oandregal]

Part of https://core.trac.wordpress.org/ticket/53175
Related to WordPress/gutenberg#31322

This PR adds support for the layout hook. Blocks can declare via supports.__experimentalLayout and themes can use the theme.json to provide the values for contentSize and wideSize.

How to test

• Add a theme with theme.json support.
• Go to the post editor, add a group block.
• Verify that there's a wp-container-ID class attached to the content and that the group block has the same class attached.

[youknowriad]

committed