Split CATCH_TRANSLATE_EXCEPTION into its own header

As far as I know, only a few users actually use it, but these changes
allow us to avoid including a surprising amount of code in the main
compilation path.

tests/SelfTest/UsageTests/Exception.tests.cpp

@@ -4,6 +4,7 @@
  */
 
 #include <catch2/catch_test_macros.hpp>
+#include <catch2/catch_translate_exception.hpp>
 #include <catch2/matchers/catch_matchers_string.hpp>
 
 #include <string>