nir: Add a nir_foreach_gl_uniform_variable helper for GL linking

There are a bunch of cases where we really do want to walk the list that
is nir->uniforms because we want all things declared "uniform" in the
GLSL.  Add a helper for this but restrict it to the GL linking code.

Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5966>
3 files changed