Shader specialization missing

[ernestask]

While loading SPIR-V shaders is possible, the resulting program fails to link due to said shaders not being specialized, which cannot be done with the current API. OpenGLRaw does expose glSpecializeShader, but that requires messing with shader indices and all.

[ernestask]

Hmm, now I see that it is actually not possible to get the ID of a shader at all, since the data constructor is hidden…