RFR: 8347620: Shenandoah: Use 'free' tag for free set related logging [v3]

[Y. Srinivas Ramakrishna]

On Tue, 14 Jan 2025 23:19:49 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Without a distinguishing tag, debug logging is too voluminous to enable when we really only want the free set's debug messages.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix merge mishap

Marked as reviewed by ysr (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/23086#pullrequestreview-2551374438