Block bindings API for 6.6

[SantosGuillamot]

Iteration of the Block bindings API tracking issue.

This is what we expect to include in WordPress 6.6. We'll use this issue to share regular updates and progress.

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• Bindings creation

Even though we'll probably won't add a UI to create bindings yet, we'd like to start discussing how it should work.

• Server APIs

• Revisit how sources access the needed context.

• Editor APIs

• Improve the existing hook implementation.
  • Block bindings: don't use hooks #60724
• Add support for allowing editing.
  • Block bindings: don't use hooks #60724
• Revisit how sources access the needed context.
  • Block Bindings: rely on broader context instead of requiring direct block context #60826
• Define how to work with placeholders.
• Add callback so sources can decide when to lock/allow editing.
• Improve the UX when the editing of bound blocks is locked.
• Define and implement UX for editing custom fields directly from blocks connected.

• Core sources

• Support editing in "Post meta" source.
  • Block bindings: allow editing post meta (new API) #60725
• Use block bindings editor API to update pattern overrides.
  • Pattern overrides: use block binding editing API #60721