* Added r.AOHistoryDistanceThreshold with default to 20, can be tweaked to avoid ghosting behind characters while not causing too much flickering
* Distance fields are now culled to each surface cache record before ray tracing for AO, saves a bit of GPU time
[CL 2496263 by Daniel Wright in Main branch]
* GetStreamOutElements is a callback function on the shadertype, just like ModifyCompilationEnvironment
* If GetStreamOutElements is specified, the FShaderResource includes that shader type in its ID as it can't be shared with any other shader type.
* FShader is no longer a FRenderResource which solves some multiple initialization issues
#codereview Marcus.Wassmer
[CL 2430024 by Daniel Wright in Main branch]
* Disabled by default, need a movable skylight with r.DistanceFieldGI enabled at load time (ConsoleVariables.ini)
* Surfels (oriented disks) are placed on mesh surfaces and capture diffuse color by evaluating the material with actual UVs and world position
* Surfels are lit and shadowed by ray tracing through mesh distance fields (directional light only so far)
* Irradiance cache records are lit with nearby Virtual Point Lights created from lit surfels. Only using camera based LOD of the surfel representation and object based surfel culling, no hierarchy yet.
* Shadowing of the VPLs is provided by distance field cone tracing. A depth visibility function is constructed along each of the 9 cone trace directions, and used to shadow the incoming VPL lighting.
* Component reregistration and transform updating causes surfels to be generated again which can be slow. In the future only the material needs to be re-evaluated.
* Geometry shaders with stream out are now supported, by implementing FShader::GetStreamOutElements
* Compute shaders can now evaluate materal attributes like BaseColor
* SkyLight MaxOcclusionDistance increased to 10m, which is the minimum useful amount for GI
[CL 2424208 by Daniel Wright in Main branch]
