Hi. I wrote a tiny plugin, SolrServiceFileInfoPlugin, (implementing SolrServiceIndexPlugin) to make filenames and file descriptions from the ORIGINAL bundle searchable.
The plugin must be added as a bean to discovery.xml.
To see it's effect, you have to reindex the Solr search core by executing:
[dspace]/bin/dspace index-discovery -b
I documented it on https://gist.github.com/MW3000/5771c0488f8952bb888357ce8c655279
Andrea Schweer and Terry Brady encouraged me to make a pull request: https://github.com/DSpace/DSpace/pull/1838