stablesort: add a 'method' argument to the debugstablesort command Let start experimenting with other way to do stable sorting.

stablesort: rename function to stablesort_branchpoint We are about to test different approach to stable sorting. We clarify that the existing method is sorting from branch points.

stablerange: update the filename to avoid cache confusion The schema validation seems to not work as well as intended, we update the file name to make sure there will be no confusion.