RFR: 8315044: GenShen: Verifier detects clean card should be dirty [v4]

[Kelvin Nilsen]

> When a Reference object is newly discovered, it is placed onto the worker's thread-local discovered list.  This sometimes results in a reference from an old object to a young object, requiring that the remembered set card-table entry be marked as dirty.  This patch causes the marking to be performed.

Kelvin Nilsen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Replace is_generational with ShenandoahCardBarrier test
 - Merge remote-tracking branch 'origin/master' into ref-processor-updates-remembered-set
 - Merge remote-tracking branch 'origin/master' into ref-processor-updates-remembered-set
 - Also update card table when moving discovered References to global list
 - Fix whitespace
 - Mark card as dirty if discovered reference list has interesting pointer

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

Changes:
  - all: https://git.openjdk.org/shenandoah/pull/314/files
  - new: https://git.openjdk.org/shenandoah/pull/314/files/597a6e02..f375d571

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=314&range=03
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=314&range=02-03

  Stats: 108 lines in 16 files changed: 48 ins; 21 del; 39 mod
  Patch: https://git.openjdk.org/shenandoah/pull/314.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/314/head:pull/314

PR: https://git.openjdk.org/shenandoah/pull/314