Fade out SSR with roughness so that it doesn't show at high roughness amounts

[clayjohn]

Fixes: #66285

This is an ad hoc change to visually match the output of ReflectionProbes, SDFGI, and VoxelGI.

Roughness: 1

Before:

After:

Roughness: 0.5

You'll notice at 0.5 roughness SSR now starts to fade out

Before:

After:

Roughness: 0.0 (no change)

Before:

After:

[Calinou]

It may also be worth adding #56804 into the mix with this PR. With this PR adding roughness fadeout, the roughness cutoff from #56804 could be decreased from 0.75 to 0.7 without losing quality (or possibly even more if you're willing to have some visible artifacting on materials with medium roughness).

[clayjohn]

It may also be worth adding #56804 into the mix with this PR. With this PR adding roughness fadeout, the roughness cutoff from #56804 could be decreased from 0.75 to 0.7 without losing quality (or possibly even more if you're willing to have some visible artifacting on materials with medium roughness).

Thats a good idea, I'll comment on #56804 with the changes needed

[BastiaanOlij]

Seems like a good way to do this

[akien-mga]

Thanks!