glsl: Parse 'layout' as a token with advanced blending or bindless

glsl: Parse 'layout' as a token with advanced blending or bindless

Both KHR_blend_equation_advanced and ARB_bindless_texture provide
layout qualifiers, and are exposed in compatibility contexts.  We
need to parse the layout qualifier as a token in order for those
to work, but forgot to extend this check.

ARB_shader_image_load_store would need a similar treatment, but we
don't expose that in legacy OpenGL contexts.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105161
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>