vk/compiler: Add shader language detection
vk/compiler: Add shader language detection

This commit adds support for the LunarG GLSL back-door as well as detecting
regular GLSL and SPIR-V.  The SPIR-V path doesn't exist yet, so that will
cause an assert-fail.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler