[crac] RFR: 8361124: [CRaC] Move recursive checkpoint test to simengine

[Timofei Pushkin]

At the moment of creation this PR includes #239 — that should be merged first. fc33e85c429536dcc89ff59afed6450bb7562639 is the change of this PR.

Makes recursive checkpoint test use `simengine` instead of `pauseengine`. Since that was the only test using `pauseengine`, a separate `PauseEngineTest` is created to test the engine.

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Commit messages:
 - Fix recursive checkpoint test
 - Make dev engines less confusing

Changes: https://git.openjdk.org/crac/pull/240/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=240&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361124
  Stats: 583 lines in 9 files changed: 312 ins; 266 del; 5 mod
  Patch: https://git.openjdk.org/crac/pull/240.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/240/head:pull/240

PR: https://git.openjdk.org/crac/pull/240