SI-7847 Static forwarders for case apply/unapply

These were excluded in f901816b3f because at the time they
were compiler fiction and translated to calls to the case
class constructor or accessors.

But since they are now bona-fide methods (albeit still occasionally
bypassed as an optimization), we can expose them conveniently to our
Java brethren.

The cut-and-pastiness of GenBCode starts to hinder maintenance.
Here's a report of further duplication that we have to fix up
post haste: https://gist.github.com/retronym/6334389
Merge pull request #2951 from retronym/ticket/7847

SI-7847 Static forwarders for case apply/unapply