Image block: disable GIF editing

[ScoutHarris]

Is your feature request related to a problem? Please describe.
With wordpress-mobile/WordPress-iOS#13803, GIF media can now be added in the editors. If added in an Image block, there is an option to edit the GIF. However, editing GIFs turn them into static images.

Describe the solution you'd like
We'd like to disable editing GIFs. (The same will be done in the classic editor as well.)

Specifically:

• Add a GIF to an image block.
• Tap on the edit icon in the upper right.
• The options menu appear, including Edit (the one we'd like to prevent).

Describe alternatives you've considered
N/A

[ScoutHarris]

ping @SergioEstevao .

[ScoutHarris]

We've decided instead to allow GIF editing, showing an alert warning the user of the consequences. Ref wordpress-mobile/WordPress-iOS#14281.