Issue: 

Page History doesn't show changes in image captions when comparing two versions via the "Compare selected versions" button.

Steps to reproduce: 

1. Create a page and add an image as an attachment.  Publish the page.
2. Now edit the page again and add a caption for the attached image. Publish the page.
3. On the view screen, navigate to "..." -> "Page History"
4. Select the two versions and click on "Compare selected versions."

Expected behavior:

The caption changes will be visible on the "Page Comparison" screen.

Actual behavior:

The captions changes are totally invisible on the "Page Comparison" screen.

Note: Despite this bug and https://jira.atlassian.com/browse/CONFCLOUD-80361, captions changes are tracked properly in Page History.  To view captions on an old page version, you must restore that version.