RFR: 8333105: Shenandoah: Results of concurrent mark may be lost for degenerated cycle

[William Kemper]

If Shenandoah does not detect a cancellation after completing concurrent mark, but before completing final mark it will fall through the concurrent cycle without collecting anything. This will shortly lead to a degenerated cycle which will _not_ use the results from the nearly complete concurrent mark. This will result in an unnecessarily longer degenerated cycle.

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Commit messages:
 - Check again for cancellation after final mark

Changes: https://git.openjdk.org/jdk/pull/19434/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19434&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333105
  Stats: 20 lines in 1 file changed: 20 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19434.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19434/head:pull/19434

PR: https://git.openjdk.org/jdk/pull/19434