RFR: Fix satb barrier for object array copy

[Kelvin Nilsen]

The satb barrier for overwritten arrays residing in old-gen must be unconditional during young GC.

During old GC, the satb barrier is only needed for overwritten old-gen arrays if the array is below TAMS within its old-gen region.

-------------

Commit messages:
 - Tidy up branch to make consistent with recompute-generation_usage PR
 - Integrate improvements to region-usage-accounting after full gc
 - Change name of phase5_restore_generation_usage
 - Fix comparison between array address and TAMS for old-gen collection
 - Merge remote-tracking branch 'GitFarmBranch/fix-satb-barrier-for-objectarray-copy' into fix-satb-barrier-for-object-array-copy
 - Restore generation budgets following fullgc
 - Fix implementation of SATB barrier for objectarray copy

Changes: https://git.openjdk.org/shenandoah/pull/237/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=237&range=00
  Stats: 121 lines in 7 files changed: 114 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/shenandoah/pull/237.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/237/head:pull/237

PR: https://git.openjdk.org/shenandoah/pull/237