Block Bindings: Try supporting custom, dynamic block attributes with role: content property

[artemiomorales]

This PR configures block bindings to process custom blocks, particularly their attributes that contain the role: content property.

How it works: When processing block attributes, the code performs a check to see if the current block being processed is from core — if not, it verifies the presence of the role: content property and, if present, allows processing to continue.

This only contains the server code — a corresponding PR for the UI can be found here in Gutenberg.

This can be tested with the following custom date block.

[github-actions]

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[github-actions]

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