glsl: Add function parameters to the parser symbol table.

glsl: Add function parameters to the parser symbol table.

In a shader such as:

    struct S { float f; }
    float identity(float S) { return S; }

we would think that "S" in "return S" referred to a structure, even
though it's shadowed by the "float S" parameter in the inner struct.

This led to the parser's grammar seeing TYPE_IDENTIFIER and getting
confused.

Fixes dEQP-GLES2.functional.shaders.scoping.valid.
function_parameter_hides_struct_type_{vertex,fragment}.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>