Keep GDScript functions in stack while yielding

This prevents GDScript functions from leaving the stack too soon when they are resuming from yield, allowing the ones expecting it to finish to know the caller.

Helps debugging cases when you use: yield(function_which_yields(), "completed") since now it shows the call that resumed that function.

Also show the function names in the debugger stack, which helps identify the stack (not sure why that was commented out, it's been like this since the first commit).