RFR: 8273626: G1: Factor out concurrent segmented array from G1CardSetAllocator [v6]

[Hamlin Li]

> To finish https://bugs.openjdk.java.net/browse/JDK-8254739, we need a segmented array to store a growing regions index array, in the initial version of that patch, a newly home made segmented array was used, but the memory efficiency is not as good as expected, G1CardSetAllocator is a potential candidate to fullfill the requirement, but need some enhancement.
> 
> This is a try to enhance G1CardSetAllocator(and G1CardSetBuffer, G1CardSetBufferList) to support element size less pointer size, and strip this basic function as a more generic segmented array (G1SegmentedArray).

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  refine code

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5478/files
  - new: https://git.openjdk.java.net/jdk/pull/5478/files/6510e8cf..992e44dd

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5478&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5478&range=04-05

  Stats: 13 lines in 5 files changed: 2 ins; 4 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5478.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5478/head:pull/5478

PR: https://git.openjdk.java.net/jdk/pull/5478