glsl: allow bindless samplers/images as out and inout parameters

glsl: allow bindless samplers/images as out and inout parameters

From section 4.1.7 of the ARB_bindless_texture spec:

   "Samplers can be used as l-values, so can be assigned into and used
    as "out" and "inout" function parameters."

From section 4.1.X of the ARB_bindless_texture spec:

   "Images can be used as l-values, so can be assigned into and used as
    "out" and "inout" function parameters."

v3: - add spec comment
    - update the glsl error message

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>