As much as it can be since the texture data is interleaved with the
model data in the files (I guess not that bad a design for 25 years ago
with the tight memory constraints), but this paves the way for
supporting sprites in Vulkan.
It now takes a context pointer (opaque data) that holds the buffers it
uses for the temporary strings. If the context pointer is null, a static
context is used (making those uses of va NOT thread-safe). Most calls to
va use the static context, but all such calls have been formatted
consistently so they are easy to find when it comes time to do a full
audit.
Where possible, symbols have been made static, prefixed with glsl_/GLSL_ or
moved into the code shared by all renderers. This will make doing plugins
easier but done now for link testing. The moving was done via the gl
commit.
