Can't call Load Stream Level in a Blueprint function

"Load Stream Level" can be called in the Event Graph of any Blueprint but it can't be called in a Blueprint Function or Function Library.

This was reported in and tested in 4.19 (CL-4033788) and reproduced in 4.20 (CL-4212847) and Main 4.21 (CL-4234136)

1. Open the UE4 Editor and create any project
2. Open the Level Blueprint
3. Create a function and try to add "Load Stream Level" to it

Results: Can't choose "Load Stream Level"

Expected: To be able to use "Load Stream Level" in a Blueprint Function