Show post meta fields in revisions panel

[SantosGuillamot]

Trac ticket:

I can see that there was a similar closed ticket for this and a related pull request.

I just left a comment in the trac ticket to discuss how to proceed here.

@adamsilverstein @Mamaduka As you discussed this in the past, it would be great to hear your opinion on the best path forward.

What?

Basically, this pull request shows the changes made to the post meta fields that have revisions enabled in the revisions UI.

Why?

For 6.6, it is planned to allow the editing of custom fields when a block is connected to them. With that, I believe it is important to show the relevant changes in the revisions.

How?

It iterates through the wp_post_revision_meta_keys, and it creates a new row in the diff for each of the meta fields that have changed.

I excluded the footnotes because it has its own section right now, but I am not sure if it should be unified in the proposed "Post Meta".

Demo

This is a quick demo of how it works after the changes in this pull request:

Post.meta.revisions.with.key.demo.mp4

---

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props santosguillamot.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.