Use StringBuilders to significantly reduce runtime. More could be done, but this seems to address the slowest part.
#jira none
#trivial
#ROBOMERGE-SOURCE: CL 17015466 in //UE5/Main/...
#ROBOMERGE-BOT: STARSHIP (Main -> Release-Engine-Test) (v839-17012307)
[CL 17015468 by jonathan adamczewski in ue5-release-engine-test branch]