Block Library: FSE Blocks: Use block context

[aduth]

Previously: #21467
Related: #21662

Context:

#21467 implements support for formal block context. This should be used in the implementation of full-site editing blocks, many of which currently either render static content, or retrieve the post context by other means (see #21662). These should be updated to retrieve entities for their respective context, using block context.

Progress:

• core/post-title (Block API: Add Block Context support #21467)
• core/post-content (Block Library: Update FSE blocks to use block context #21696) (resolved in FSE: Add entity editor to post content block #22473)
• core/post-author (Block Library: Update FSE blocks to use block context #21696)
• core/post-comments (Block Library: Update FSE blocks to use block context #21696)
• core/post-comments-count (Block Library: Update FSE blocks to use block context #21696)
• core/post-comments-form (Block Library: Update FSE blocks to use block context #21696)
• core/post-date (Block Library: Update FSE blocks to use block context #21696)
• core/post-excerpt (Block Library: Update FSE blocks to use block context #21696)
• core/post-featured-image (Block Library: Update FSE blocks to use block context #21696)
• core/post-tags (Block Library: Update FSE blocks to use block context #21696)
• core/site-title (Block Library: Update FSE blocks to use block context #21696)
• core/template-part (Block Library: Update FSE blocks to use block context #21696)

[aduth]

Reopening since #21696 only updated the server-side implementation.

Client-side will still require revisions, largely to reimplement the existing blocks to avoid using useEntityProp in most cases in favor of a combination of (a) block context and (b) core-data entities.

An example reference is #22359, updating the Post Author block to use block context in the client-side implementation.

[ntsekouras]

Closing as all of the tasks have been merged.