[Common] Fix ClassLoaderUtils dynamic classpath on JDK 9+

[shangeyao]

Problem

On JDK 9+, the system class loader is not a URLClassLoader and the ucp field lives on a superclass. ClassLoaderUtils.addURL throws NoSuchFieldException: ucp, breaking Hadoop conf directory loading.

Proposed solution

• Try TCCL and system class loader in order
• Walk the class hierarchy to locate ucp on JDK 9+ built-in loaders
• Keep URLClassLoader.addURL path for older JDKs

[shangeyao]

Closing because related PR #4399 was closed without merge. Work is not being pursued on this branch at the moment.