For Forward ES31
Default SceneColor RG11B10 + R16F\32F Depth texture
With PropagateAlpha on RGBA16F + R16F\32F
PostProcess we sample SceneDepthAux for Depth
For Deferred ES31
SceneDepthAux only for Metal
PropagateAlpha not working yet
PostProcess we sample SceneDepthTexture for Depth
cvar to change Depth texture from 16 to 32Fr.Mobile.SceneDepthAux
cvar for AlphaPropagate r.Mobile.PropagateAlpha
#jira UE-98033
#rb Dmitriy.Dyomin, Carl.Lloyd, Jack.Porter
[CL 16644095 by Florin Pascu in ue5-main branch]