Set names on classloaders

[DaveCTurner]

We create a hierarchy of classloaders, but it's rather challenging in a debugger to work out which one is which. Could we give them more descriptive names to indicate where they're coming from? Today their names look to be the default jdk.internal.loader.Loader @2faf6e4a etc.

[elasticsearchmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[rjernst]

I investigated this a bit. Although we do create our own URLClassLoader instances in tests (when we run with the classpath), in production we create Java module layers for each ES plugin/module, and each of those in turn create their own loaders. We may still be able to tweak this by providing our own loader, but it will require a larger refactoring than just changing the ctor called.