Add image editing functionality to REST API for media attachments

[the-hercules]

What?

Closes

Closes #78077

What?

Add lineage tracking for cropped media created through the Gutenberg/REST image edit flow by storing _source_attachment_id on newly created derivative attachments.

Why?

When Gutenberg crops an image, it creates a brand new attachment instead of updating the existing one. While the generated attachment metadata already stores the immediate source in parent_image, there is no stable root/original lineage reference across crop-of-crop chains.

This makes it difficult to:

• identify all derivatives of an original image
• distinguish the root original from intermediate crops
• support future restore/grouping workflows cleanly

This PR adds a minimal backward-compatible MVP for derivative lineage tracking using attachment post meta.

How?

This PR adds a compatibility helper, wp_get_original_attachment_id(), that returns the root/original attachment ID for an attachment derivative tree, or the attachment’s own ID when no lineage meta exists.

It also overrides the Gutenberg REST media edit flow in Gutenberg_REST_Attachments_Controller::edit_media_item() so that when a new cropped attachment is created, it stores _source_attachment_id on the new attachment. The stored value is always the root/original attachment ID, not the immediate parent crop.

This keeps the two lineage concepts separate:

• _source_attachment_id stores the root/original attachment ID
• parent_image['attachment_id'] in _wp_attachment_metadata continues to store the immediate source attachment ID

The change is limited to newly created cropped attachments and does not backfill or migrate existing media.

Testing Instructions

1. Activate the Gutenberg plugin in your local environment.
2. Open the Site Editor or Post Editor.
3. Insert an Image block.
4. Upload a new image and note its attachment ID.
5. Use the block toolbar crop tool to crop the image and save the change.
6. Identify the new cropped attachment ID in the database.
7. Confirm the cropped attachment has a _source_attachment_id row in wp_postmeta pointing to the original attachment ID.
8. Confirm the cropped attachment’s _wp_attachment_metadata still contains parent_image['attachment_id'] pointing to the immediate source attachment.
9. Crop the newly cropped image again to create a second derivative.
10. Confirm the second derivative’s _source_attachment_id still points to the original root attachment ID.
11. Confirm the second derivative’s parent_image['attachment_id'] points to the first cropped attachment, not the original.
12. Upload a separate image without cropping it.
13. Confirm that normal uploads do not get a _source_attachment_id meta entry.

[github-actions]

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[github-actions]

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Co-authored-by: the-hercules <thehercules@git.wordpress.org>
Co-authored-by: andrewserong <andrewserong@git.wordpress.org>
Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>

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[github-actions]

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[ramonjd]

Superseded by #81803