[lworld] RFR: 8357373: [lworld] jdk/valhalla/valuetypes/ObjectMethods.java fails with -XX:+UseAtomicValueFlattening

[Roger Riggs]

This test failing with VM options prompted a refatoring and cleanup of the test (and renaming to be more appropriate).
The test is re-enabled with a 4 combinations of command line flags.

Refactored test to verify that hashcode changed with each change to a field. Previously, the test tried to compute the hashCode for the value class. That was fragile in the presence of the VM changing the layout information. Check the hashCodes are equal for objects that are `.equals`. Renamed to 'ValueObjectMethodsTest`.

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Commit messages:
 - JDK-8357373: [lworld] jdk/valhalla/valuetypes/ObjectMethods.java fails with -XX:+UseAtomicValueFlattening

Changes: https://git.openjdk.org/valhalla/pull/1771/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1771&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357373
  Stats: 687 lines in 2 files changed: 354 ins; 333 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1771.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1771/head:pull/1771

PR: https://git.openjdk.org/valhalla/pull/1771