RFR: 8367731: G1: Make G1CollectionSet manage the young gen cset group [v3]

[Ivan Walulya]

On Tue, 23 Sep 2025 09:54:21 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> 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 incrementally with one additional commit since the last revision:
> 
>   * failed to save file with changes

Marked as reviewed by iwalulya (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/27312#pullrequestreview-3257330872