Add textarea context for every failing function

When a function in the function engine ( lang/funcs/dage/ ) fails, I want to be able to print the precise "textarea" context to know which line of code that function was called/defined from. We need to plumb through this information from the AST so that we'll know the line number that the error corresponds to. We'd also like to show the code snippet from the textarea. The canonical example is the panic() function which would make finding the precise line of code easier.