Lightmap resources were not recreated correctly when when the feature level changed. Also, modified FRenderResource::ChangeFeatureLevel() so that it doesn't recreate resources which are already using the correct feature level.
#jira UE-79367
#rb daniel.wright
#lockdown cristina.riveron
#ROBOMERGE-SOURCE: CL 8376524 in //UE4/Release-4.23/...
#ROBOMERGE-BOT: RELEASE (Release-4.23 -> Main) (v406-8472469)
[CL 8498103 by mihnea balta in Main branch]