OpenXML: Support codefinder

Suggested by Jonathan here, but this is also something we could be interested in (especially for Word)

  1. The ability to use a codefinder with Word/Powerpoint/Excel. The Excel filter does already allow for subfiltering, which it's great, especially when dealing with chunks of embedded HTML/MD, but I think it would be practical to also have a codefinder (for scenario where the only prep required is for a bunch of patterns to be tagged).