RFR: 8276299: G1: Unify the wording buffer/node/element in G1SegmentedArrayXxx, G1CardSetXxx and related classes [v2]

[Hamlin Li]

> Currently, the words "buffer", "node" and "element" are used together in G1SegmentedArrayXxx, G1CardSetXxx and related classes in an inconsistent way, which is very unfavorable for understanding.
> 
> We should not confuse buffer and node together, and not confuse node and element together. The new wording should be based on something like the following rule:
> 
> segmented array (1) -- segment (N) -- slot (M)

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

  Thomas review

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6605/files
  - new: https://git.openjdk.java.net/jdk/pull/6605/files/06212003..a86760ef

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6605&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6605&range=00-01

  Stats: 5 lines in 3 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6605.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6605/head:pull/6605

PR: https://git.openjdk.java.net/jdk/pull/6605