Make reporter lookup case insensitive, registration case preserving

Previously registration was case preserving, but lookup used
lowercased reporter name, so a reporter whose name contained
upper case character could not be requested by the user.

tests/ExtraTests/X23-CasingInReporterNames.cpp

@@ -0,0 +1,40 @@
+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE_1_0.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+/**\file
+ * Test that reporter registration is case-preserving, selection is
+ * case-insensitive.
+ *
+ * This is done by registering a custom reporter that prints out a marker
+ * string upon construction and then invoking the binary with different
+ * casings of the name.
+ */
+
+#include <catch2/reporters/catch_reporter_streaming_base.hpp>
+#include <catch2/catch_reporter_registrars.hpp>
+
+#include <iostream>
+
+class TestReporter : public Catch::StreamingReporterBase {
+public:
+    TestReporter(Catch::ReporterConfig const& _config):
+        StreamingReporterBase(_config) {
+        std::cout << "TestReporter constructed\n";
+    }
+
+    static std::string getDescription() {
+        return "Reporter for testing casing handling in reporter registration/selection";
+    }
+
+    ~TestReporter() override;
+};
+
+TestReporter::~TestReporter() = default;
+
+CATCH_REGISTER_REPORTER("testReporterCASED", TestReporter)
+