Improve the files report source (MDL-75535) to allow reporting/filtering on the file 'contenthash' property, in order to allow for the detection of multiple uses of the same file across the site

Currently we can report and aggregate on all file data, but it doesn't account for the fact that the Files API de-duplicates files when they are uploaded to multiple contexts/components (causing them to be counted multiple times in custom reports). The 'contenthash' value (both as a column and filter) will aid reporting for administrators