RFR: 8325516: Shenandoah: Move heap change tracking into ShenandoahHeap [v3]

[Aleksey Shipilev]

On Thu, 8 Feb 2024 21:36:08 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Shenandoah sets a flag when new regions are allocated or retired. This flag currently resides in the control thread. Moving it into the heap reduces code duplication with upcoming generational mode changes.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve comment for heap_changed field

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17777#pullrequestreview-1871811738