[clang-tidy] Restore test parameter operator<< function (NFC)

Clang erroneously flagged the function as "unused", but it is most
definitely used by gtest to pretty print the parameter value when
a test fails.

Make the pretty printing function a friend function in the parameter
class similar to other clang unit tests.

clang-tools-extra/unittests/clang-tidy/ModernizeModuleTest.cpp

@@ -48,6 +48,11 @@ namespace {
 struct Param {
   bool Matched;
   const char *Text;
+
+  friend std::ostream &operator<<(std::ostream &Str, const Param &Value) {
+    return Str << "Matched: " << std::boolalpha << Value.Matched << ", Text: '"
+               << Value.Text << "'";
+  }
 };
 
 class MatcherTest : public ::testing::TestWithParam<Param> {};