glave: move code-gen'ed files.
glave: move code-gen'ed files.

* glave-generate.py has moved into tools/glave/scripts/ and renamed to vk_generate.py
* still reference xgl.py and xgl_helper.py from GL-Next directory.
* all glave-specific code-gen'ed files now live in the source tree
* all glave-specific code-gen'ed files are now generated into a "codegen" directory local to the project to make it easier to spot when a generated file has changed or is being debugged.
* all glave-specific code-gen'ed files are now being checked in so that we can better track differences caused by the code-gen as the header file evolves.

(based on squash of the follow two cherry-picks, plus some additional changes to remove files generated by xgl_helper.py since they change every build)
(cherry picked from commit eec461f4bc68c5ac12a6b73b9f6e5464be0640bf)
(cherry picked from commit 2614252bfc3fe9c2cd8470b3b42b529a69f2e3f3)

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools