Lit Shader Graph compatible with both URP and HDRP

For standard PBR materials, we should use a shader that works in both URP and HDRP. This is especially important for the asset library since otherwise, we'll need to create every material twice.

As far as I know, it's possible with shadergraph to target both URP and HDRP. The question is whether we can easily access the mask maps in URP (and probably other things).

@Roland09 do you have any experience with this?