Simplify SystemDictionary::is_shared_class_visible

The current implementation of SystemDictionary::is_shared_class_visible and SystemDictionaryShared::is_shared_class_visible_for_classloader are very hard to follow:

http://hg.openjdk.java.net/jdk/jdk/file/6bcfcb7fe83b/src/hotspot/share/classfile/systemDictionary.cpp#l1175
http://hg.openjdk.java.net/jdk/jdk/file/6bcfcb7fe83b/src/hotspot/share/classfile/systemDictionaryShared.cpp#l661

Maybe we can simplify the logic to:

SystemDictionary::is_shared_class_visible(Symbol* class_name,
                                               InstanceKlass* ik,
                                               Handle class_loader, TRAPS)
find {runtime_module, runtime_location, runtime_loader} that can define ik now;

find {dumptime_module, dumptime_location, dumptime_loader} that defined ik during CDS dump time;

if ({runtime_module, runtime_location, runtime_loader} ==
    {dumptime_module, dumptime_location, dumptime_loader}) {
   return true;
} else {
   return false;
}