This backports some CDS related fixes and improvements:
- Build machinery to build _coh CDS archives, those are generated with +UCOH and are selected by default when running with +UCOH. This is similar to how we create and use _nocoops archives.
- Some adjustments in tests to deal with the _coh CDS archive (including some reversals of earlier changes which are no longer necessary).
- A bugfix in the ArchiveHeapWriter which would sometimes write invalid narrowKlass with +UCOH.