Adding new IBM extended charsets

[Martin Buchholz]

History:  I recall 15 years ago wondering why no one from IBM was
maintaining the IBM charsets in the jdk.  Today anything but UTF-* is
increasingly legacy, so the case for including them is weaker than back
then.  Probably today the IBM charsets are best maintained outside the jdk
sources as a third party package, especially considering that openjdk has
been kicking some other components like corba out of the nest.

But there is some synergy - some of the openjdk charset tests check
invariants that apply to all charset implementations.  I may have even
fixed some IBM charset code many years ago.