Block JSON schema: Add layout.allowCustomContentAndWideSize field

[t-hamano]

Related to #56236

What?

This PR adds a supports.layout.allowCustomContentAndWideSize field to the schema of block.json.

Why?

To enhance the developer experience.

Testing Instructions

Create a JSON file like the one below and open it in a code editor.

{
	"$schema": "https://raw.githubusercontent.com/WordPress/gutenberg/block-schema/add-allow-custom-content-and-wide-size/schemas/json/block.json",
	"name": "test/test",
	"title": "Test",
	"supports": {
		"layout": {}
	}
}

You should see allowCustomContentAndWideSize reference.

Screenshots or screencast

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Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: fabiankaegy <fabiankaegy@git.wordpress.org>

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[fabiankaegy]

Thanks for adding this :)

[t-hamano]

@fabiankaegy Thanks for the review!