RFR: Account for humongous object waste

[Y. Srinivas Ramakrishna]

On Thu, 13 Apr 2023 22:37:54 GMT, William Kemper <wkemper at openjdk.org> wrote:

> The unused portion of the last region in a humongous object is now tracked and logged.

Looks good modulo previous comment re documentation clarification(s). 🚢

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Marked as reviewed by ysr (Author).

PR Review: https://git.openjdk.org/shenandoah/pull/255#pullrequestreview-1388789537