As a user, I want validate to throw an error when more than one primary product references the same physical file

[smclaughlin7]

Issue an error when more than one primary basic product label in a collection define the same physical file. (Should this be reclassified as a bug?)

For example when producing document collections, it is rather common to duplicate an existing label as a template for another primary document product but then forget to change <file_name> to specify the correct physical file. This results in one document file being defined by two different primary product labels and therefore two different LIDVIDs. At best, the Validation Tool reports a warning that one physical file in the document collection is not associated with a label. Since the Validation Tool seems to already check if each physical file is labeled, it should also check if each physical file is defined by more than one primary product label in the collection.

Applicable Requirements:

• 🦄 #248
• 🦄 #755