Add kernel test coverage for FileReferenceResolver

Problem/Motivation

#1452100: Private file download returns access denied, when file attached to revision other than current recently was committed but only contains functional test coverage for uploading files to nodes. While this does test the FileReferenceResolver service I think it would be wise to add additional, specific test coverage for the service. This will give us greater confidence to refactor this service.

Also seems like we may be missing coverage for some of the nuanced revision and translation handling, the service is rather complex.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet