There's duplicated code for searching unsupported system properties in

 CDSConfig::check_unsupported_dumping_properties() and
 CDSConfig::check_unsupported_cds_runtime_properties

https://github.com/openjdk/jdk/blob/da8a095a19c90e7ee2b45fab9b533a1092887023/src/hotspot/share/cds/cdsConfig.cpp#L263-L305

Consolidate the code and rename the C++ functions to reflect what they actually do.