RFR: JDK-8297796 GenShen: instrument the remembered set scan [v12]

[Y. Srinivas Ramakrishna]

On Mon, 19 Dec 2022 23:56:23 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> I mean percentage where I said `%ge`. I'll clarify the comments a bit more. Please continue the review and I'll improve some of the documentation comments for clarity.
>
> Got it - I had `age` on my brain.

Slightly reworded some of the code comments for greater clarity.

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PR: https://git.openjdk.org/shenandoah/pull/176