This is needed by TAMER's template desugaring. The XSD is superceded by `nir::parse`, but can't go away until TAMER fully supplants the XSLT-based compiler. ...and after all this time, I still never got rid of the duplicate XSD. Or even recall which one is the duplicate. DEV-13708
This directory exists for compatibility with earlier build scripts and path assumptions before TAME was extracted into its own repository. A full transition will remove this directory.