RFR: 8328220: GenShen: Move generational mode operational parameters out of ShenandoahHeap

[William Kemper]

* Many fields previously defined in `ShenandoahHeap` have been moved to `ShenandoahOldGeneration`.
* Generational specific serviceability has been moved to `ShenandoahGenerationalHeap`.
* Methods for sizing the old generation have been moved to `ShenandoahGenerationalHeap`.
* `ShenandoahGenerationalHeap::heap()` now asserts that the generational mode is active.

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Commit messages:
 - Pre-PR review cleanup
 - Improve comment
 - So long ShenandoahCollectionSetParameters, we hardly new ye
 - Find better homes for evacuation reserves
 - Move generational memory pools into shGenHeap
 - Move surplus/deficit calculations into shGenHeap
 - Move card marking for old evacuations to old generation
 - Move reporting of failed promotion from heap to old gen
 - Move failed old gen evac flag from heap to old gen
 - Fix issues
 - ... and 4 more: https://git.openjdk.org/shenandoah/compare/e9a1c699...00f8778b

Changes: https://git.openjdk.org/shenandoah/pull/406/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=406&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328220
  Stats: 1425 lines in 24 files changed: 646 ins; 661 del; 118 mod
  Patch: https://git.openjdk.org/shenandoah/pull/406.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/406/head:pull/406

PR: https://git.openjdk.org/shenandoah/pull/406