Add debug primitive providing current source location + enclosing function #2133

While developing a scenario, it would be useful for debugging to be able to see which function a system robot is currently "in" as it executes its program.

Sometimes to achieve this I have placed a say "function_name"; at the top of each function in a robot's program (i.e. "printf debugging") to accomplish this. But it would be nice to have an automatic mechanism.

I imagine it is feasible:

• At program parse time, annotate each Term with the closest "function definition" that contains it.
• At runtime, inspect the top frame of the robot's machine and display the function name for the currently focused term in the F2 dialog.