SSRNode: Honor metalness.

[Mugen87]

Related issue: #29597, #21487

Description

This makes sure metalness is not just an on/off switch for SSR but actually influences the intensity. The lighting of the example is a bit updated so it better fits to PBR materials.

We might want to honor even more parameters (see #28752) but for now it's a good start.

[ligaofeng0901]

Why is only the metalness factor taken into account? Does it mean there is no SSR effect on the fragment that metalness is zero? In ssr( colorNode, depthNode, normalNode, metalnessNode, camera ) , metalnessNode must be a texture node, what about make it be any type of node? so we can pass the param like max(metalness, roughness.oneMinus()).

[Mugen87]

As mentioned in #28752, honoring more material properties is wanted but I guess there are some uncertainties in doing it in a PBR conform way. I suggest we continue the discussion in #28752 and try to find a solution to include roughness in the SSR code.

Ideally, we have some sort of reference/documented resource that we implement (I have not checked so far if the formula proposed in #28752 (comment) is correct).