Added FunctionLibrary and FunctionReferenceNode classes
Implemented support and validation for those in the Controller
Implemented unit test for checking the validity of a FunctionReferenceNode.
#rb jack.cai
#jira UEA-564
[CL 15000860 by Helge Mathee in ue5-main branch]
Implementation of relevant nodes for collapse feature, controller + actions as well as unit test
To be audited by Jack.Cai
#jira UEA-564
#rb na
#fyi jack.cai
[CL 14815556 by Helge Mathee in ue5-main branch]