RFR: 8319198: GenShen: Old at end of Full GC must include newly promoted objects

[Kelvin Nilsen]

At end of Full GC, remember live bytes after last old-gen mark after promotions are completed rather than immediately after old marking is completed.  This is a more accurate representation of old live.  This reduces the likelihood that we will need to immediately trigger another old-gen GC following the Full GC.

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Commit messages:
 - Record old-gen live after promotion is done

Changes: https://git.openjdk.org/shenandoah/pull/350/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=350&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319198
  Stats: 4 lines in 1 file changed: 3 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/shenandoah/pull/350.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/350/head:pull/350

PR: https://git.openjdk.org/shenandoah/pull/350