RFR: 8315044: GenShen: Verifier detects clean card should be dirty

[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.

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Commit messages:
 - Fix whitespace
 - Mark card as dirty if discovered reference list has interesting pointer

Changes: https://git.openjdk.org/shenandoah/pull/314/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=314&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315044
  Stats: 17 lines in 1 file changed: 17 ins; 0 del; 0 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