enforce that Intel genxml is sorted

First, I've made a few cleanups to the script with an eye at making it faster. Then I added a tag it didn't know about, then added a validation mode, and added meson tests for the xml.

The purpose of this is to help make updating the xml more seamless, since newly generated updates can also be sorted, easy the problems of git rebase conflicts. The cleanups were in part to help me understand the script better, and second to make it faster when run as a meson test.