RFR (M): 8233306: Sort members in G1's HeapRegion after removal of Space dependency

[Thomas Schatzl]

Hi all,

  after the change to HeapRegion in JDK-8233306 the declaration fo the 
HeapRegion class is a bit messed up (merging G1ContiguousSpace, adding a 
few members needed from ContiguousSpace).

This change tries to fix this as much as possible by shuffling around 
stuff (i.e. grouping allocation related methods, evacuation related 
methods, some helper pointers in HeapRegion, etc).

Depends on JDK-8189737 also out for review.

CR:
https://bugs.openjdk.java.net/browse/JDK-8233306
Webrev:
http://cr.openjdk.java.net/~tschatzl/8233306/webrev/
Testing:
hs-tier1-5

Thanks,
   Thomas