glsl: Add parsing support for multi-stream output in geometry shaders.

glsl: Add parsing support for multi-stream output in geometry shaders.

This implements parsing requirements for multi-stream support in
geometry shaders as defined in ARB_gpu_shader5.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>