RFR: 8264851: Shenandoah: Rework control loop mechanics to use timed waits

[Aleksey Shipilev]

On Thu, 25 Sep 2025 20:35:59 GMT, William Kemper <wkemper at openjdk.org> wrote:

> We use a similar mechanism in `shGenerationalControlThread` already. Using a timed wait allows the control thread to be woken up before the wait expires.

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/27502#pullrequestreview-3314374701