scripts: Add helper file generator
scripts: Add helper file generator

This vk.xml generator will create the enum_string_helper header file,
as well as the other vk_helper.py-generated files in the future.

Change-Id: Ia19a2c6fd23c1df2af3ded66e2e80b88159a7d85

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