[jdk17u-dev] RFR: 8322503: Shenandoah: Clarify gc state usage

[William Kemper]

Resolved trivial conflicts.

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Commit messages:
 - 8322503: Shenandoah: Clarify gc state usage

Changes: https://git.openjdk.org/jdk17u-dev/pull/2298/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2298&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322503
  Stats: 26 lines in 5 files changed: 8 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2298.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2298/head:pull/2298

PR: https://git.openjdk.org/jdk17u-dev/pull/2298