RFR: 8349094: GenShen: Race between control and regulator threads may violate assertions

[William Kemper]

Not clean. Several follow up issues here.

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Commit messages:
 - 8352299: GenShen: Young cycles that interrupt old cycles cannot be cancelled
 - 8351464: Shenandoah: Hang on ShenandoahController::handle_alloc_failure when run test TestAllocHumongousFragment#generational
 - 8352091: GenShen: assert(!(request.generation->is_old() && _heap->old_generation()->is_doing_mixed_evacuations())) failed: Old heuristic should not request cycles while it waits for mixed evacuation
 - 8352428: GenShen: Old-gen cycles are still looping
 - Backport 3a8a432c05999fe478b94de75b416404b5a515d2

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/174/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=174&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349094
  Stats: 980 lines in 19 files changed: 334 ins; 295 del; 351 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/174.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/174/head:pull/174

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/174