RFR: 8329350: GenShen: Do not reset mark bitmaps on a safepoint

[William Kemper]

Clean backport

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Commit messages:
 - Backport f43034d8d1dc571390f357dc3617f376cafa085f

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/37/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=37&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329350
  Stats: 173 lines in 12 files changed: 101 ins; 57 del; 15 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/37.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/37/head:pull/37

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/37