RFR: 7904039: jcstress: Rework Dekker tests to include reference types

[Aleksey Shipilev]

[JDK-8351997](https://bugs.openjdk.org/browse/JDK-8351997) shows there is a gap in testing: we only verify Dekker-style scenarios over primitive volatiles. We need to extend this to reference types.

There is a larger amendment to include reference types in seqcst-generator tests.

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Commit messages:
 - Whitespace
 - Missing test
 - More
 - Fix

Changes: https://git.openjdk.org/jcstress/pull/169/files
  Webrev: https://webrevs.openjdk.org/?repo=jcstress&pr=169&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904039
  Stats: 130 lines in 7 files changed: 53 ins; 70 del; 7 mod
  Patch: https://git.openjdk.org/jcstress/pull/169.diff
  Fetch: git fetch https://git.openjdk.org/jcstress.git pull/169/head:pull/169

PR: https://git.openjdk.org/jcstress/pull/169