RFR: 8368152: Shenandoah: Incorrect behavior at end of degenerated cycle [v4]

[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 comments and names

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27456/files
  - new: https://git.openjdk.org/jdk/pull/27456/files/2324450a..4c36c6f3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27456&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27456&range=02-03

  Stats: 32 lines in 3 files changed: 5 ins; 10 del; 17 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