RFR: 8336742: Shenandoah: Add more verbose logging/stats for mark termination attempts

[William Kemper]

Not clean.

-------------

Commit messages:
 - Backport 90527a57848f452be3be089a703cbc2af2d1657a

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/126/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=126&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336742
  Stats: 23 lines in 5 files changed: 10 ins; 1 del; 12 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/126.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/126/head:pull/126

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/126