Disable editing GIFs in the classic editor.

[ScoutHarris]

Ref ##13803 (comment)

This removes the ability to edit a GIF when added to a post/page via the classic editor. The block editor will be updated with WordPress/gutenberg#23036.

To test:

• Create a new post or page.
• Switch to the classic editor.
• Insert media, and select Free GIF Library.
• Select a GIF. Wait for it to finish loading.
• Tap on the GIF.
• Verify Edit does not appear in the options list.

GIF options	Image options

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger an installable build for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[ScoutHarris]

@SergioEstevao requested we just show an alert in both editors notifying the user that the animations will be lost upon editing, instead of preventing editing altogether.