RFR: 8368152: Shenandoah: Incorrect behavior at end of degenerated cycle [v3]

[William Kemper]

> 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

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Improve comment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27456/files
  - new: https://git.openjdk.org/jdk/pull/27456/files/c962f198..2324450a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27456&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27456&range=01-02

  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27456.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27456/head:pull/27456

PR: https://git.openjdk.org/jdk/pull/27456