GEMS18 — Move normative schemas from the spec to separate machine-readable files

For the GEMS 1.7 RTF, the AB asked if we can move the normative schemas from the specification document to separate machine-readable files for the next GEMS RTF, and this ticket serves to capture that request.

This applies to the normative schemas in the XML and JSON PSMs; there are no applicable schemas in the ASCII PSM to be moved. Any non-normative snippets would remain in the specification as references or examples.

Identify a repository to manage the files such as GitHub, like is done for GDDI. Does the final version need to be submitted with the Spec update to OMG to be added on the OMG Spec Version page?