Bug 38330

Needed for issue #38306 - from the Ant module, I
need to load Ant tasks from a named module, using
a class loader derived from the module loader.
Using the SystemClassLoader is not really safe as
it is common for there to be multiple copies of
important libraries in the VM and you would have
no way of knowing which you were getting.

Proposed added API in o.o.m.ModuleInfo:

/**
 * Get a class loader associated with this module
 * that can load classes defined in the module.
 * You can only call this method on an enabled
 * module, and the result may change if the module
 * is disabled and reenabled.
 * The class loader may or may not be shared with
 * any other module, or be the application's
 * startup class loader, etc.
 * @return a module class loader
 * @throws IllegalArgumentException if this module
 *         is disabled
 */
public abstract ClassLoader getClassLoader();

o.n.c.m.Module would rename its current
getClassLoader to getClassLoaderOrNull and
implement this method to throw IAE as appropriate.

Note that the addition of an abstract method to
this class is not an incompatible API change since
it already forbids there to be subclasses except
in core.