mesa/st: Move the vec4 type size function into core GLSL types.

mesa/st: Move the vec4 type size function into core GLSL types.

The only bit that gallium varied on was handling of bindless.  We can
retain previous behavior for count_attribute_slots() by passing in
"true" (though I suspect this is just giving a silly answer to a silly
question), and delete our recursive function from mesa/st.

Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3297>