[Workbench] In the collections page, provide the ability to select individual files from different collections and combine them into a new collection.
Since clippy is no longer supported, we now have no way of selecting individual files and combining them into a new collection. We would need to create multiple collections and select all those collections instead.
It would be nice if we can do this in collections page.
Performance concern: It might be too expensive to list all files of all collections in the collections. It probably is desirable that we add "+" column to the existing collections page that expands the collection when clicked and offers checkboxes for individual files in that expanded collection.