[jfx19] RFR: 8291588: Update boot JDK to 18.0.2

[Ambarish Rapte]

Update Boot JDK to 18.0.2.
Tested build on all platforms and full test run on MacOS Catalina.

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Commit messages:
 - 8291588: Update boot JDK to 18.0.2

Changes: https://git.openjdk.org/jfx/pull/857/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=857&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291588
  Stats: 11 lines in 2 files changed: 0 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jfx/pull/857.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/857/head:pull/857

PR: https://git.openjdk.org/jfx/pull/857