Blocks: Update schema to require either a type or an enum

[walbo]

Description

Part of #35902.

The attribute definition will contain, at a minimum, either a type or an enum. There may be additional fields.

Update the block.json schema to require either a type or an enum prop.

How has this been tested?

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[fabiankaegy]

Didn't know this was possible :) Thanks for the fix (y)

[gziolo]

Thank you for the fix 👍🏻

#36264 updates the template lock attribute to use both the type and enum.

In practice, both type and enum are completely optional. I assume it has to stay this way for backward compatibility. However, for the schema, we could be more strict. The current proposal is quite reasonable unless we want to always enforce the type which wouldn't be a bad idea. I have just noticed that the type should also allow an array of types.

[walbo]

Yes. After I created this PR I discovered an issue with only having enum on SSR blocks (see #36319), so enforcing type would be great.