Remove all use of std::integral_constant from functors

This MR removes all use of std::integral_constant from the functor code base -- they were being used to provide constructor arguments whose sole role was to allow non-type template arguments to be deduced. With this MR, these arguments are specified to be template arguments directly. As this was the last use of std::integral_constant, it is also removed from the grammar used to generate the C++ functor code.