This is later used to build static mesh derived data in cases where Nanite coarse mesh representation replaces original static mesh data and we can't depend on it. In extreme cases it lowers main thread derived data build time from ~7.5s to ~0.1s.
#rb Richard.TalbotWatkin
[CL 14578414 by Krzysztof Narkowicz in ue5-main branch]
Contains all work on Lumen since shipping Reverb in March:
* New Opaque Final Gather with higher quality in clean architecture and better performance
* Improved global tracing which reduces leaking
* New basic Reflections pipeline which respects material Roughness
* New HZB traces that are more accurate at tracing against the depth buffer
* Hardware Ray Tracing paths for Lumen shadowing and Final Gather
#rb none
[CL 14274844 by Daniel Wright in ue5-main branch]
