gl2: merge usage of FaceCulling
internal/glutil: remove invalid comment
gl2: merge usage of BlendState and StencilState
gl2: merge usage of DepthCmp
gl2: merge usage of stencil write masks
gl2: merge usage of color write mask booleans
gl2: merge usage of state booleans
gl2: use helper function for many glEnable/glDisable calls