RFR: 8289389: Fix warnings: type should also implement hashCode() since it overrides Object.equals()

[Andy Goryachev]

- added missing hashCode() methods

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Commit messages:
 - 8289389: implemented missing hashCode()

Changes: https://git.openjdk.org/jfx/pull/821/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=821&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289389
  Stats: 81 lines in 9 files changed: 70 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jfx/pull/821.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/821/head:pull/821

PR: https://git.openjdk.org/jfx/pull/821