added get_vtable_offset_args to chugin api

[nshaheed]

This lets you find a function definition with a specific argument list (i.e. now you can look for SinOsc.freq() when SinOsc.freq(float f) is the first in the overload list of SinOsc.freq.

Here's an example usage:

// Call getter function
CK_DLL_SFUN(patch_call) {
  Chuck_Object* obj = (Chuck_Object*)GET_NEXT_OBJECT(ARGS);
  Chuck_String *method = (Chuck_String *)GET_NEXT_STRING(ARGS);

  // Get object to find offset from
  Chuck_DL_Api::Type obj_type = API->object->get_type( obj );
  Chuck_Type * t = (Chuck_Type *)obj_type;

  string method_str = API->object->str(method);

  // Want the getter, so the args list is empty
  Chuck_Type * arg_list[] = {};
  
  // Lookup the specific function definition, normally this would return the setter
  t_CKINT offset =
    API->type->get_vtable_offset_args(VM, obj_type, method_str.c_str(), arg_list, 0);  

  if (offset < 0) {
    string message = "Member function " + method_str + "() not found in object " + string(API->type->base_name(obj_type));
    API->vm->throw_exception("MemberFunctionNotFound", message.c_str(), SHRED);
  }

  Chuck_DL_Arg* arg = new Chuck_DL_Arg();

  Chuck_DL_Return ret =
      API->vm->invoke_mfun_immediate_mode(obj, offset, VM, SHRED, arg, 0);

  RETURN->v_float = ret.v_float;
}