RFR: Fix satb barrier for object array copy [v3]

[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.

Kelvin Nilsen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:

 - Merge remote-tracking branch 'github/master' into fix-satb-barrier-for-object-array-copy
 - Fix typo in comment
 - 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
   
   Original code ommitted SATB barrier for old-gen arrays that were above
   the old-gen TAMS.  That was an error.

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Changes: https://git.openjdk.org/shenandoah/pull/237/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=237&range=02
  Stats: 50 lines in 2 files changed: 43 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