The G1CollectedHeap methods to get information about the heap reservation have several issues:
- named inconsistently, sometimes they have a "region" suffix, sometimes they do not have a "reserved" in it at all
- sometimes they are virtual for no reason
- some are just cluttering up the G1CollectedHeap interface, i.e. there seems to be too little gain to have them (e.g. single use or used unnecessarily)

Fix this up a little.