RFR: 8364934: G1: Rename members of G1CollectionSet [v5]

[Thomas Schatzl]

> Hi all,
> 
>   please review this renaming of various members of `G1CollectionSet` to
> 
> - use the same prefixes for the regions ("_regions") and candidate groups ("_groups") consistently, avoiding adding prefixes here and there for no discernible reason
> - remove unnecessary prefixes (`collection_set`) - everything is part of the collection set
> - fix/improve some documentation
> 
> Testing: gha
> 
> Thanks,
>   THoams

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  * undo unnecessarily added JDK-8365040

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26670/files
  - new: https://git.openjdk.org/jdk/pull/26670/files/889b0875..88eca31a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26670&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26670&range=03-04

  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26670.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26670/head:pull/26670

PR: https://git.openjdk.org/jdk/pull/26670