Support function pointers as arguments of function pointers

[Oleg Rakhmatulin]

The current implementation of the inline signature parser handles all native types, user-defined types, and even generics correctly. The only possible use case that is not handled by this implementation is function pointers inside the function pointers. So construction like this will not be processed:

delegate*<int, delegate*<int, int>, int>

The second argument of this function pointer is the function pointer itself and now such recursive construction is not supported. In fact, I'm unable to find any example or practical use case for such a callback-in-callback approach but if someone can provide it I'll be happy to spend time implementing it.