RFR: 8358340: Support CDS heap archive with Generational Shenandoah

[Aleksey Shipilev]

On Mon, 2 Jun 2025 18:22:36 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Now that [JDK-8364111](https://bugs.openjdk.org/browse/JDK-8364111) is integrated, Generational Shenandoah can support CDS heap loads. This also allows Generational Shenandoah to work well with Leyden/AOT. We allocate things in young regions, and there is nothing else in the heap, so no card table updates are necessary.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah` 
>  - [x] Linux x86_64 server fastdebug, `runtime/cds` with `-XX:+UseShenandoahGC -XX:ShenandoahGCMode=generational`
>  - [x] Linux x86_64 server fastdebug, `runtime/cds` with `-XX:+UseShenandoahGC -XX:ShenandoahGCMode=generational -XX:+ShenandoahVerify`

Thanks! Here goes.

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PR Comment: https://git.openjdk.org/jdk/pull/25597#issuecomment-3142755055