RFR: 8368152: Shenandoah: Incorrect behavior at end of degenerated cycle

[William Kemper]

On Tue, 23 Sep 2025 19:59:05 GMT, William Kemper <wkemper at openjdk.org> wrote:

> There are several issues addressed in this PR:
> * Shenandoah always ran a full GC after any degenerated cycle
> * The number of consecutive degenerated GCs with bad progress was reset for every degenerated cycle
> * Good progress was reported in generational mode even when no progress is made

There is a comment in `shDegeneratedGC` explaining this scenario. I'll move it to `shCollectorPolicy`. I didn't quite understand why single-gen mode would not benefit equally from this reasoning, but I tried to preserve the original intended behavior.

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PR Comment: https://git.openjdk.org/jdk/pull/27456#issuecomment-3325562835