Optimize calls to SystemDictionaryShared::define_shared_package for classpath

A related RFE JDK-8241815 handles the module image case.
This RFE is for handling the jar in the shared classpath case.

For the shared classpath case, the SystemDictionaryShared::define_shared_package calls up to java BuiltInClassLoader::defineOrCheckPackage. It is sufficient to call define_shared_package once per element in the classpath.

An idea is to add an int field to PackageEntry. Use the n-th bit to indicate that we have checked the n-th element in the shared classpath. This would handle up to 32 elements in the classpath.