RFR: Use whole number of regions when resizing generations

[Kelvin Nilsen]

On Fri, 13 Jan 2023 00:45:38 GMT, William Kemper <wkemper at openjdk.org> wrote:

> This avoids overflowing calculations when using a 32 bit word - it also simplifies some of the operations. All of the github actions are succeeding now.

Thanks.

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Marked as reviewed by kdnilsen (Committer).

PR: https://git.openjdk.org/shenandoah/pull/199