externals: Add catch2 v3.2.1

Merge commit '6879e5bb1c' as 'externals/catch'

externals/catch/tests/SelfTest/helpers/parse_test_spec.cpp

@@ -0,0 +1,22 @@
+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+#include <helpers/parse_test_spec.hpp>
+
+#include <catch2/internal/catch_test_spec_parser.hpp>
+#include <catch2/interfaces/catch_interfaces_tag_alias_registry.hpp>
+
+namespace Catch {
+
+    TestSpec parseTestSpec( std::string const& arg ) {
+        return TestSpecParser( ITagAliasRegistry::get() )
+            .parse( arg )
+            .testSpec();
+    }
+
+} // namespace Catch