RFR: 8338620: GenShen: Distinguish between young and old collector in GC configuration [v2]

[Kelvin Nilsen]

On Tue, 20 Aug 2024 18:57:12 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Return `ShenandoahYoung` for `young_collector` under generational mode (continue returning `N/A` for other modes). Return `ShenandoahOld` for `old_collector` under generational mode (continue returning `Shenandoah` for other modes).
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix minimal variant build

Marked as reviewed by kdnilsen (Committer).

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PR Review: https://git.openjdk.org/shenandoah/pull/477#pullrequestreview-2249131737