RFR: 8332095: GenShen: Move more generational mode members out of shHeap [v3]

[William Kemper]

> The following members and methods in shHeap are only used in generational mode and can be moved out of common code:
> * ShenandoahHeap::cancel_old_gc
> * ShenandoahHeap::transfer_old_pointers_from_satb
> * ShenandoahHeap::_is_aging_cycle

William Kemper has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:

 - Merge remote-tracking branch 'shenandoah/master' into move-shenandoah-heap-fields
 - Merge remote-tracking branch 'shenandoah/master' into move-shenandoah-heap-fields
 - Update confusing comment
 - Move is_aging_cycle into genshen heap
 - Move 'cancel_old_gc' from shHeap into shOldGeneration
 - Inline forwarding method ShenandoahHeap::transfer_old_pointers_from_satb

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Changes: https://git.openjdk.org/shenandoah/pull/431/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=431&range=02
  Stats: 101 lines in 11 files changed: 39 ins; 44 del; 18 mod
  Patch: https://git.openjdk.org/shenandoah/pull/431.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/431/head:pull/431

PR: https://git.openjdk.org/shenandoah/pull/431