Style Revisions: Offer comparison views

[jameskoster]

Observing the changes between style revisions is not always easy, especially if they are subtle. Let's explore how to improve this experience by offering:

• A side by side visual comparison.
• A diff tool, similar to the current post revision interface. (There is some initial exploratory work around this in Global Styles: Add link to compare revisions #52829).

[ramonjd]

Thanks for opening this!

Copying over some idea/links from previous discussion for reference:

Discussed in:

• Global Styles: Add link to compare revisions #52829 (comment)
• Global styles: add revisions UI #50089 (comment)
• Global styles: add revisions UI #50089 (comment)

It's possible to use WordPress's existing revisions.php page to compare the global styles custom post, however it means comparing changes to JSON, which may not be accessible to everyone.

As mentioned previously, it is possible to load two versions in two iframes:

2023-05-01.16.16.51.mp4

@c4rl0sbr4v0 has also explored a comparison engine to diff two theme.json trees: tenberg/pull/52829#issuecomment-1659027089

We probably need to undertake more investigation in order to balance performance and utility.

As a starting taster will might like to display top-level changes to the user, e.g.,