RFR: 8367731: G1: Make G1CollectionSet manage the young gen cset group [v2]

[Thomas Schatzl]

> Hi all,
> 
>   please review this change that lets the collection set manage the young cset candidate group directly. Currently everywhere the collection set (not "containing" the young cset candidate group) is used, we immediately do the same thing for the young gen candidate group in the same place.
> 
> This makes it kind of natural to put together (and the `G1CollectionSet` already manages adding new regions to the young gen cset group anyway, so that split in responsibility is questionable anyway).
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into 8367731-g1collectionset-manage-young-gen-group
 - * comment update
 - * let collectionset manage the young regions group card set

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Changes: https://git.openjdk.org/jdk/pull/27312/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27312&range=01
  Stats: 65 lines in 8 files changed: 26 ins; 29 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/27312.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27312/head:pull/27312

PR: https://git.openjdk.org/jdk/pull/27312