Support Image Widget fully in page data form

Overview

Image props use the media library widget, but an entity can still have an image field and as a result use the image widget.

There's at least one problem with this ATM - the Alternative text field is not editable. Other issues might surface once that is addressed.

Proposed resolution

• get the alternative text field working
• Address any other issues that surface after alt text is fixed
• Provide e2e tests that confirm things work. File upload might not be possible with e2e (at least not easily). If this is the case perhaps the setup script can provide some of the needed scenarios.

User interface changes