optimized shaders to use SvPosition where possible, following change could remove some unused interpolator
[CL 2697164 by Martin Mittring in Main branch]
GBufferResources were being used in TranslucentShadowDepthPS but not being set. They shouldn't be set as GBuffers aren't valid for this draw.
A similar issue occured a while ago in which the SceneTextureParameters were being used here and caused artefacts in the translucent shadows based on the SceneColor.
I avoided this by setting them to a dummy black texture. This approach won't work for the GBufferResources so I've removed that fix and gone about things differently.
The shader sets a define to have SceneTextureLookup() just return black.
This means the SceneTextures, nor the GBufferResources need be set at all for this draw.
[CL 2651076 by Simon Tovey in Main branch]
#ttp 346312 - Pri 0 - Do Not Leave Desk (blocker!)) TTP #346312 was assigned to Nick Penwarden (BLOCKER: CRITICAL: Regression: Many particles with translucent or additive materials do not render correctly
#codereview Nick.Penwarden
[CL 2293882 by Simon Tovey in Main branch]
