feat: sanitize illegal XML characters from outgoing messages (upstream 189050f3)

tests/unittests/test_common.h

@@ -34,3 +34,4 @@ void prof_whole_occurrences_tests(void** state);
 void prof_occurrences_of_large_message_tests(void** state);
 void unique_filename_from_url_td(void** state);
 void format_call_external_argv_td(void** state);
+void str_xml_sanitize__strips_illegal_characters(void** state);