RFR: 8329699: GenShen: Move promotion logic out of shHeap and shHeapRegion

[William Kemper]

Clean backport.

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Commit messages:
 - Backport 9d869ca1b4d5b210a93dbb4d209189d913c92446

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/39/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=39&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329699
  Stats: 1876 lines in 36 files changed: 968 ins; 791 del; 117 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/39.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/39/head:pull/39

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/39