Googletest export

Do not use std::result_of as it was removed in C++20.

PiperOrigin-RevId: 303783600

googlemock/include/gmock/gmock-actions.h

@@ -970,7 +970,8 @@ struct InvokeMethodWithoutArgsAction {
   Class* const obj_ptr;
   const MethodPtr method_ptr;
 
-  using ReturnType = typename std::result_of<MethodPtr(Class*)>::type;
+  using ReturnType =
+      decltype((std::declval<Class*>()->*std::declval<MethodPtr>())());
 
   template <typename... Args>
   ReturnType operator()(const Args&...) const {