RFR: 8328220: GenShen: Move generational mode operational parameters out of ShenandoahHeap

[Kelvin Nilsen]

On Thu, 14 Mar 2024 21:46:14 GMT, William Kemper <wkemper at openjdk.org> wrote:

> * Many fields previously defined in `ShenandoahHeap` have been moved to `ShenandoahOldGeneration`.
> * Generational specific serviceability has been moved to `ShenandoahGenerationalHeap`.
> * Methods for sizing the old generation have been moved to `ShenandoahGenerationalHeap`.
> * `ShenandoahGenerationalHeap::heap()` now asserts that the generational mode is active.

Thank you so much for this much needed refactoring.  This was a lot of careful and thorough work.

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Marked as reviewed by kdnilsen (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/406#pullrequestreview-1943184924