scripts: Add generation of struct_size_helper header
scripts: Add generation of struct_size_helper header

Added generator-side plumbing to create the vk_struct_size_helper.h
file.

Change-Id: I5ff226131b8db2d773e4422877bdb2993ed76cf4

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