RFR: 8334315: Shenandoah: reduce GC logging noise

[duke]

On Wed, 19 Jun 2024 15:11:52 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

> Qualify certain log messages as ergo or debug to remove extraneous noise from regular gc logs.

@kdnilsen 
Your change (at version 2a74ecc458cdadf86ab72e96776fbd04c3d0def0) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk/pull/19795#issuecomment-2253036972