alt text disapears for File field type (Images) when importing template to library

Problem/Motivation

Blocks that contain the File field type (Images) lose their alternative text when saved to a template library.

Steps to reproduce

Add a block that contains a File Field (IMAGE) with Alt text. Click ADD TO LIBRARY. Then IMPORT FROM LIBRARY the new saved template into a new section. The image appears without the alt text.

Proposed resolution

Include alt text when saving template to library

Remaining tasks

User interface changes

API changes

Data model changes