glsl: re-enable varying packing in GL4.4+
glsl: re-enable varying packing in GL4.4+

We can still do packing we just need to get the packing type from the consumer
rather than the producer.

Reviewed-by: Iago Toral Quiroga <a847aabaac44184372f6b1cd1a59aa254daaeb0b@igalia.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97033

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler