Googletest export

Remove bool_constant in favor of std::integral_constant<bool, ...>;
The one non-trivial use of bool_constant has been changed to have significantly
fewer template specializations.

PiperOrigin-RevId: 275842490

googletest/include/gtest/internal/gtest-internal.h

@@ -855,8 +855,7 @@ class GTEST_API_ Random {
 // true if and only if T is type proto2::Message or a subclass of it.
 template <typename T>
 struct IsAProtocolMessage
-    : public bool_constant<
-          std::is_convertible<const T*, const ::proto2::Message*>::value> {};
+    : public std::is_convertible<const T*, const ::proto2::Message*> {};
 
 // When the compiler sees expression IsContainerTest<C>(0), if C is an
 // STL-style container class, the first overload of IsContainerTest