jmx-dev RFR: 8358624: ImmutableDescriptor violates equals/hashCode contract after deserialization

[Kevin Walls]

Hashcode needs to be reset to -1 to force its recalculation on next call, after deserialization.

The change in the readResolve() method is the fix for this problem.  While here I added similar lines in other methods that may update fields (although these are noted as not supported, they change a class named "immutable).

Added a test.  There is a test for serialization for this class, but I found it clearer to add the test for this specific recently discovered issue in its own test file.

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Commit messages:
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 - 8358624: ImmutableDescriptor violates equals/hashCode contract after deserialization

Changes: https://git.openjdk.org/jdk/pull/25758/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25758&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358624
  Stats: 82 lines in 2 files changed: 82 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25758.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25758/head:pull/25758

PR: https://git.openjdk.org/jdk/pull/25758