Block Bindings in WordPress 7.0

Supersedes #67520.

Enhancements

• Filter available source items for a given attribute by format.
  • See this preliminary exploration and discussion.
  • We'll do this in close collaboration with @oandregal, who's approaching formats for the Fields API. See the tracking issue and this example.
• https://github.com/WordPress/gutenberg/issues/64870
  • Related exploration: https://github.com/WordPress/gutenberg/pull/72391
  • Take two: https://github.com/WordPress/gutenberg/pull/73889

Explorations

• Bind multiple attributes to a single source. Example: Bind Image block's url, alt, title attributes to post's featured image (exposed via core/post-data source).
  • Related exploration: https://github.com/WordPress/gutenberg/pull/71002
• Try binding a block that requires a "repeater" concept. Example: Bind Gallery block to list of images.
• Streamline the API based on recurring usage patterns in getValues and getFieldsList.
  • Examples include passing more arguments to them (e.g. block name, attributes); or providing additional ways for a block source to communicate that it will not expose and source items for a given block, attribute, or other context. (Things that are currently done by e.g. returning [] from getFieldsList, based on certain criteria.)
• https://github.com/WordPress/gutenberg/issues/73461
• Remove requirement to define a block bindings source both on the server and client side. Instead, allow server-side only definition, and communicate to the client. See this comment, bullet point 4, for a suggestion how to do this.
• https://github.com/WordPress/gutenberg/issues/73423

Bug Fixes

• https://githu