This work is the start of producing a Java-domain Throwable
hierarchy that matches the Ruby hierarchy, so that Ruby exceptions
can be caught using their actual Throwable type rather than using
RaiseException and checking the exceptions type manually.

A few changes of note:

* RubyException has most logic moved up to new
  AbstractRubyException.
* All RubyException now hold a reference to their RaiseException,
  created lazily once as needed.
  * Throw a Ruby exception using the form
    `throw ex.getRaiseException()`.
  * Provide construction logic specific to a given exception by
    overriding createRaiseException.
* The nativeException parameter is eliminated from all exception
  construction and initialization paths. It was unused.

This forms the meat of wiring up the new parallel exception
hierarchy. All public constructors of RaiseException are now
deprecated and unused. RaiseException.from() forms take their
place and know how to properly construct a Ruby exception and
wrap it with an appropriate RaiseException subclass.

Three native exceptions are added, mapping to the Ruby exception
type of the same name: Exception, StandardError, and
SignalException.

One location in the code that caught RaiseException is now able
to catch StandardError (RubyNumeric coerce logic). There are
likely others.

See #4781.

This includes everything in standard Ruby plus our additions but
minus the errno classes.

See #4781.