Post Images: look for images in inner blocks.

[jeherve]

Fixes #13338

Changes proposed in this Pull Request:

Until now, we only parsed blocks that included images right away. However, some blocks may include some other, inner, blocks.
Let's go 2 levels deep to look for blocks that we support and that may include images.

This allows us to support, for example, a colunms block that would include an image block as well as a text block.

Testing instructions:

• Start on a site without this patch, with the Sharing module active.
• In a new post, add an image block and upload a large image. Publish your post.
• View the post, and view source.
• Search for an og:image meta tag. It should list your image.
• Now start a new post.
• Insert a Columns block. In that block, insert a Paragraph block as well as an image block. Add the same image as before to your image block.
• Publish the post, view it, view source.
• Search for an og:image meta tag. Your image is not listed.
• Apply the patch.
• Note that og:image meta tags now work even with posts with columns blocks.

You can repeat this with Gallery blocks, tiled galleries, slideshows, all inside columns blocks.

You can also try installing the Kadence Blocks – Gutenberg Page Builder Toolkit plugin, and insert a Row layout block instead of a columns block. See that everything keeps working.

Proposed changelog entry for your changes:

• Post Images: look for representative images in inner blocks.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello jeherve! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D32151-code before merging this PR. Thank you!

[matticbot]

jeherve, Your synced wpcom patch D32151-code has been updated.

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: October 1, 2019.
Scheduled code freeze: September 24, 2019

Generated by 🚫 dangerJS against f7b0cb0

[matticbot]

jeherve, Your synced wpcom patch D32151-code has been updated.

[kraftbj]

One gap I discovered in testing is the core/media-text block. This block is unique in that it is a nested block, but the ID of the media is part of the parent block's attribute—not an inner block.

I added a commit to handle this, so leaving as needs review for at least that second commit. Approving it so @jeherve can be that reviewer of my change. :)

[jeherve]

This looks good to me, thanks for the addition! Merging.