XWIKI-9309: Also search in attachments when type is DOCUMENT
* Index attachment author, date and size
* Make sure we can sort attachment results by file name, author, date and size
* Duplicate attachment data on document index rows (using multiValued fields, so the relation between various attachment meta data is lost -- we won't know that a file size corresponds to a file name)
* Add media type, author, date and size facets for attachments.
* Refactor (and improve) DocumentSolrMetadataExtractorTest