UETOOL-213 - Minimize Slate FString -> FText conversion (remove SLATE_TEXT_ATTRIBUTE)
This fixes any editor/engine specific code that was passing text to Slate as FString rather than FText.
[CL 2399803 by Jamie Dale in Main branch]
Made sure everything was using FText rather than FString, and also updated the property editor API to return tooltips as FText rather than FString.
[CL 2373917 by Jamie Dale in Main branch]
UE-4821 - Deleting a material node in the latest fortnite build causes a crash without a crash log
I wasn't able to reproduce this crash, but from looking at the logs and the code, it seems this likely failed due to the property handle becoming invalid. I've added some checks to better handle this case.
[CL 2354612 by Jamie Dale in Main branch]
