Expose files attached to releases to views

Subtask of #76726: Refactor project module to use Views [meta issue] which will allow us to do lots of good things, including replacing the hard-coded download table with a view: we need to expose the information about the files attached to release nodes to views. So long as #179471: release file attachments should use drupal upload functionality isn't done (which will be D7 at the earliest), we need to export this info ourselves.