[crac] RFR: 8364931: [CRaC] Stabilize recompiler tests

[Timofei Pushkin]

Stabilizes recompiler tests:
- `NaturalDecompilationTest` now ensures the method is not enqueued for another compilation before proceeding with the test.
- In `RecompilationFlagsTest` recompilation waiting period of a predefined length is replaced with waiting for the methods to get enqueued and dequeued to/from the compilation queue.

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Commit messages:
 - Update error message
 - Make recompiler tests more stable

Changes: https://git.openjdk.org/crac/pull/259/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=259&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364931
  Stats: 104 lines in 2 files changed: 67 ins; 16 del; 21 mod
  Patch: https://git.openjdk.org/crac/pull/259.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/259/head:pull/259

PR: https://git.openjdk.org/crac/pull/259