Step Functions: recursive functions

[sam-goodwin]

Add support for recursive functions into Step Functions.

• [ ] allow FunctionDecl within a FunctionDecl
• [ ] allow it to be called - resulting in its states being included in the state machine, perhaps like a macro?
• [ ] implement the behavior of lexical scope and stack frames
• [ ] tail recursion

[thantos]

https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_stepfunctions.StateMachineFragment.html