RFR: 7902989: jcstress: Add samples for high-level race conditions [v8]

[Michael Mirwaldt]

> I have created two more samples:
> 
> - one sample for read-modify-write-sequences
> - one sample for check-then-react-sequences

Michael Mirwaldt has updated the pull request incrementally with one additional commit since the last revision:

  renamed temp vars v1 to t1 and v2 to t2

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Changes:
  - all: https://git.openjdk.java.net/jcstress/pull/88/files
  - new: https://git.openjdk.java.net/jcstress/pull/88/files/6bb1a6af..a855c79a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jcstress&pr=88&range=07
 - incr: https://webrevs.openjdk.java.net/?repo=jcstress&pr=88&range=06-07

  Stats: 12 lines in 1 file changed: 0 ins; 0 del; 12 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/88.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/88/head:pull/88

PR: https://git.openjdk.java.net/jcstress/pull/88