glsl/parser: Extract version directive processing into a function.

glsl/parser: Extract version directive processing into a function.

Version directive handling is going to have to be used within two
parser rules, one for desktop-style version directives (e.g. "#version
130") and one for the new ES-style version directive (e.g. "#version
300 es"), so this patch moves it to a function that can be called from
both rules.

No functional change.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Carl Worth <cworth@cworth.org>