Short circuit post-content rendering for revisions (#26593)

[bobbingwide]

Description

When using Appearance > Templates to edit a template I was experiencing out of memory errors.
I tracked this down to infinite recursion while attempting to render revisions in the REST API processing for templates.
I found that the easiest fix was to short circuit the rendering for revisions.
This seemed to have no side effect on the editor; compare revisions still worked.

How has this been tested?

• I reproduced the problem in a new WordPress Multi Site site with Twenty Twenty-One Blocks.
• I applied the fix and rebuilt using npm run dev
• I retried the step to edit the template.
• It succeeded.
• I viewed Revisions to see my changes.

Screenshots

Types of changes

Fixes #26593

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

I could not PHPUnit test the solution as I don't have a wp-env environment.

[skorasaurus]

@bobbingwide ;
#26593 has been fixed (which this issue addresses) so I'm closing this;

Please reopen if you think the PR is fulfilling something still not yet resolved