glsl: Reference data structure ctors in grammar

glsl: Reference data structure ctors in grammar

We now tie the grammar to the ctors of the ASTs they reference.

This requires that we actually have definitions of the ctors.

In addition, we also need to define "print" and "hir" methods for the AST
classes. The Print methods are pretty simple to flesh out. However, at this
stage of the development, we simply stub out the "hir" methods and flesh
them out later.

Also, since actual class instances get returned by the productions in the
grammar, we also need to designate the type of the productions that
reference those instances.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>