Make dict2inst to work with arbitrary _init parameters

This is achieved by skipping initializer call while creating an instance
of a GDScript. This is implemented by passing -1 as an argument count
to `_new` and interpreting any value below 0 to mean that the initializer
should not be called during instantiation, because internal members of
an instance are going to be overridden afterwards.

modules/gdscript/gdscript_functions.cpp

@@ -1153,8 +1153,7 @@ void GDScriptFunctions::call(Function p_func, const Variant **p_args, int p_arg_
 					return;
 				}
 			}
-
-			r_ret = gdscr->_new(nullptr, 0, r_error);
+			r_ret = gdscr->_new(nullptr, -1 /*skip initializer*/, r_error);
 
 			if (r_error.error != Variant::CallError::CALL_OK) {
 				r_ret = Variant();