Add UnpackStructImpl for structs with 21 fields.

PiperOrigin-RevId: 731737844
Change-Id: I3efeb26b0bf179958c8a3eda0b55dfc3d7778fb9

Author: Abseil Team

googlemock/include/gmock/gmock-matchers.h

@@ -3305,6 +3305,13 @@ auto UnpackStructImpl(const T& u, std::make_index_sequence<20>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t] = u;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t);
 }
+template <typename T>
+auto UnpackStructImpl(const T& in, std::make_index_sequence<21>, char) {
+  const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u] =
+      in;
+  return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t,
+                  u);
+}
 #endif  // defined(__cpp_structured_bindings)
 
 template <size_t I, typename T>