RFR: 8325659: Normalize Random usage by incubator vector tests

[Evgeny Nikitin]

Improve RNG usage in said tests:

1. The RNG is not created by our Utils class, as suggested in our JTReg tests;
2. The seed, accordingly, is not a fixed value now, but truly random;
3. The tests that had been creating their own Random instances, are now using RAND static member from the AbstractVectorTest;
4. The generated tests sources have been re-generated.

The most important change is #2, it could add variability and help cover more JIT Compiler and Runtime scenarios.

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Commit messages:
 - Adjust generated tests
 - Use class member RNG vs newly created one
 - 8325659: Normalize Random usage by incubator vector tests

Changes: https://git.openjdk.org/jdk/pull/18675/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18675&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325659
  Stats: 469 lines in 69 files changed: 188 ins; 0 del; 281 mod
  Patch: https://git.openjdk.org/jdk/pull/18675.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18675/head:pull/18675

PR: https://git.openjdk.org/jdk/pull/18675