[gtest] Drop custom-rolled heterogeneous comparator functors in favor of C++ standard ones

* Standard heterogeneous comparator functors such as `std::equal_to<>` and `std::less<>` [have been available since C++14](https://en.cppreference.com/w/cpp/utility/functional/less_void)
* Now that [C++14 is the minimum supported version of C++ in Googletest](https://github.com/google/oss-policies-info/blob/main/foundational-cxx-support-matrix.md), let's delete these duplications of the standard library

PiperOrigin-RevId: 515743068
Change-Id: I1563a2f94039c3a6688429298555545a922f6d7e

googlemock/include/gmock/gmock-matchers.h

@@ -257,6 +257,7 @@
 
 #include <algorithm>
 #include <cmath>
+#include <functional>
 #include <initializer_list>
 #include <ios>
 #include <iterator>
@@ -1199,27 +1200,27 @@ class PairMatchBase {
   };
 };
 
-class Eq2Matcher : public PairMatchBase<Eq2Matcher, AnyEq> {
+class Eq2Matcher : public PairMatchBase<Eq2Matcher, std::equal_to<>> {
  public:
   static const char* Desc() { return "an equal pair"; }
 };
-class Ne2Matcher : public PairMatchBase<Ne2Matcher, AnyNe> {
+class Ne2Matcher : public PairMatchBase<Ne2Matcher, std::not_equal_to<>> {
  public:
   static const char* Desc() { return "an unequal pair"; }
 };
-class Lt2Matcher : public PairMatchBase<Lt2Matcher, AnyLt> {
+class Lt2Matcher : public PairMatchBase<Lt2Matcher, std::less<>> {
  public:
   static const char* Desc() { return "a pair where the first < the second"; }
 };
-class Gt2Matcher : public PairMatchBase<Gt2Matcher, AnyGt> {
+class Gt2Matcher : public PairMatchBase<Gt2Matcher, std::greater<>> {
  public:
   static const char* Desc() { return "a pair where the first > the second"; }
 };
-class Le2Matcher : public PairMatchBase<Le2Matcher, AnyLe> {
+class Le2Matcher : public PairMatchBase<Le2Matcher, std::less_equal<>> {
  public:
   static const char* Desc() { return "a pair where the first <= the second"; }
 };
-class Ge2Matcher : public PairMatchBase<Ge2Matcher, AnyGe> {
+class Ge2Matcher : public PairMatchBase<Ge2Matcher, std::greater_equal<>> {
  public:
   static const char* Desc() { return "a pair where the first >= the second"; }
 };

googletest/include/gtest/gtest-matchers.h

@@ -40,6 +40,7 @@
 #define GOOGLETEST_INCLUDE_GTEST_GTEST_MATCHERS_H_
 
 #include <atomic>
+#include <functional>
 #include <memory>
 #include <ostream>
 #include <string>
@@ -178,43 +179,6 @@ class MatcherInterface : public MatcherDescriberInterface {
 
 namespace internal {
 
-struct AnyEq {
-  template <typename A, typename B>
-  bool operator()(const A& a, const B& b) const {
-    return a == b;
-  }
-};
-struct AnyNe {
-  template <typename A, typename B>
-  bool operator()(const A& a, const B& b) const {
-    return a != b;
-  }
-};
-struct AnyLt {
-  template <typename A, typename B>
-  bool operator()(const A& a, const B& b) const {
-    return a < b;
-  }
-};
-struct AnyGt {
-  template <typename A, typename B>
-  bool operator()(const A& a, const B& b) const {
-    return a > b;
-  }
-};
-struct AnyLe {
-  template <typename A, typename B>
-  bool operator()(const A& a, const B& b) const {
-    return a <= b;
-  }
-};
-struct AnyGe {
-  template <typename A, typename B>
-  bool operator()(const A& a, const B& b) const {
-    return a >= b;
-  }
-};
-
 // A match result listener that ignores the explanation.
 class DummyMatchResultListener : public MatchResultListener {
  public:
@@ -758,50 +722,53 @@ class ComparisonBase {
 };
 
 template <typename Rhs>
-class EqMatcher : public ComparisonBase<EqMatcher<Rhs>, Rhs, AnyEq> {
+class EqMatcher : public ComparisonBase<EqMatcher<Rhs>, Rhs, std::equal_to<>> {
  public:
   explicit EqMatcher(const Rhs& rhs)
-      : ComparisonBase<EqMatcher<Rhs>, Rhs, AnyEq>(rhs) {}
+      : ComparisonBase<EqMatcher<Rhs>, Rhs, std::equal_to<>>(rhs) {}
   static const char* Desc() { return "is equal to"; }
   static const char* NegatedDesc() { return "isn't equal to"; }
 };
 template <typename Rhs>
-class NeMatcher : public ComparisonBase<NeMatcher<Rhs>, Rhs, AnyNe> {
+class NeMatcher
+    : public ComparisonBase<NeMatcher<Rhs>, Rhs, std::not_equal_to<>> {
  public:
   explicit NeMatcher(const Rhs& rhs)
-      : ComparisonBase<NeMatcher<Rhs>, Rhs, AnyNe>(rhs) {}
+      : ComparisonBase<NeMatcher<Rhs>, Rhs, std::not_equal_to<>>(rhs) {}
   static const char* Desc() { return "isn't equal to"; }
   static const char* NegatedDesc() { return "is equal to"; }
 };
 template <typename Rhs>
-class LtMatcher : public ComparisonBase<LtMatcher<Rhs>, Rhs, AnyLt> {
+class LtMatcher : public ComparisonBase<LtMatcher<Rhs>, Rhs, std::less<>> {
  public:
   explicit LtMatcher(const Rhs& rhs)
-      : ComparisonBase<LtMatcher<Rhs>, Rhs, AnyLt>(rhs) {}
+      : ComparisonBase<LtMatcher<Rhs>, Rhs, std::less<>>(rhs) {}
   static const char* Desc() { return "is <"; }
   static const char* NegatedDesc() { return "isn't <"; }
 };
 template <typename Rhs>
-class GtMatcher : public ComparisonBase<GtMatcher<Rhs>, Rhs, AnyGt> {
+class GtMatcher : public ComparisonBase<GtMatcher<Rhs>, Rhs, std::greater<>> {
  public:
   explicit GtMatcher(const Rhs& rhs)
-      : ComparisonBase<GtMatcher<Rhs>, Rhs, AnyGt>(rhs) {}
+      : ComparisonBase<GtMatcher<Rhs>, Rhs, std::greater<>>(rhs) {}
   static const char* Desc() { return "is >"; }
   static const char* NegatedDesc() { return "isn't >"; }
 };
 template <typename Rhs>
-class LeMatcher : public ComparisonBase<LeMatcher<Rhs>, Rhs, AnyLe> {
+class LeMatcher
+    : public ComparisonBase<LeMatcher<Rhs>, Rhs, std::less_equal<>> {
  public:
   explicit LeMatcher(const Rhs& rhs)
-      : ComparisonBase<LeMatcher<Rhs>, Rhs, AnyLe>(rhs) {}
+      : ComparisonBase<LeMatcher<Rhs>, Rhs, std::less_equal<>>(rhs) {}
   static const char* Desc() { return "is <="; }
   static const char* NegatedDesc() { return "isn't <="; }
 };
 template <typename Rhs>
-class GeMatcher : public ComparisonBase<GeMatcher<Rhs>, Rhs, AnyGe> {
+class GeMatcher
+    : public ComparisonBase<GeMatcher<Rhs>, Rhs, std::greater_equal<>> {
  public:
   explicit GeMatcher(const Rhs& rhs)
-      : ComparisonBase<GeMatcher<Rhs>, Rhs, AnyGe>(rhs) {}
+      : ComparisonBase<GeMatcher<Rhs>, Rhs, std::greater_equal<>>(rhs) {}
   static const char* Desc() { return "is >="; }
   static const char* NegatedDesc() { return "isn't >="; }
 };