Show original document title (and filename?) before importing

When importing annotations into a document, it would be useful if the Import dialog provided some confirmation of which document the annotations were originally created on, to guard against accidentally importing annotations from the wrong document.

This was originally taken from https://github.com/hypothesis/client/issues/5743#issuecomment-1693194981:

> Try to include the "original document" (Title? Name?) on the export file, so that we can display that information before importing, helping users catch possible mistakes while importing from the wrong document.