Reduce use of void* in generated native wrapper functions

[enlight]

There's actually no real reason to use void* in native wrapper function return values and parameters. For example, the first argument to every native wrapper function is void* self, but there's no reason why this can't just be UObject* self, sizeof(void_) == sizeof(UObject_) anyway, which is all that matters. Likewise with any other pointer parameters or return values, getting rid of the void* means a few extra casts can be eliminated too.