Many of the cardtable interfaces and class hierarchy were designed
at a time when HotSpot was still growing up and designed  as a vehicle
for research and evolution. This has, however, resulted in much avoidable
cruft and convoluted class hierarchies that serve no real purpose
in a commercial product JVM. They make code comprehension and
maintenance expensive and can also make finding, diagnosing and
finding bugs difficult, as well as leaving performance on the table.

This CR is aimed at cleaning up this accumulated cruft from the
classes. See comments section for the specific details.