vk: Copy current header to vulkan-0.138.2.h
vk: Copy current header to vulkan-0.138.2.h

While upgrading Mesa to the new 0.170.2 API, it's convenient to have all
three headers available in the tree:
    - vulkan-0.138.2.h, the old one
    - vulkan-0.170.2.h, the new one
    - vulkan.h, the one in transition

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler