RFR: Coalesce and fill old, pinned regions after old gen final mark [v5]

[William Kemper]

> Pinned regions were not being coalesced and filled. This fixes a crash observed with the specjbb 2015 benchmark.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Fix whitespace

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/149/files
  - new: https://git.openjdk.org/shenandoah/pull/149/files/561e5e90..9f569892

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=149&range=04
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=149&range=03-04

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/149.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah pull/149/head:pull/149

PR: https://git.openjdk.org/shenandoah/pull/149