Updated FTextBuilder to use this to join several generated lines together, rather than building a single FString which loses all the localization information.
Note: FTextBuilder will now consistently add a line when any of its AppendLine functions are called, whereas previously it may have done nothing if the builder was empty and indentation was disabled.
#rb Francis.Hurteau
#ROBOMERGE-OWNER: ryan.vance
#ROBOMERGE-AUTHOR: jamie.dale
#ROBOMERGE-SOURCE: CL 5740279 via CL 5740280 via CL 5740281 via CL 5745290 via CL 5745350
#ROBOMERGE-BOT: DEVVR (Main -> Dev-VR)
[CL 5751116 by jamie dale in Dev-VR branch]
9cd9bd5eac