Rename outer function parameters in handler macros

[Bob Aman]

Right now if you have the function definitions in your handler named something like _request and you try to use request, you'd expect to get an error about it being the wrong variable name. Instead you get can't capture dynamic environment in a fn item because of how the handler macro wraps the inner function. This could lead to confusion so the outer function parameters should be renamed in a way that is much less likely to collide, and additionally should be named in a way that's still readable but won't cause the compiler to get clever with any naming suggestions it might make.