RFR: 8324270: Update boot JDK to 21.0.2

[Ambarish Rapte]

JDK 21.0.2 is now released : https://jdk.java.net/21/
Did a full CI build including Webkit and executed all headful tests.

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Commit messages:
 - boot jdk 21.0.2

Changes: https://git.openjdk.org/jfx/pull/1345/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1345&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324270
  Stats: 11 lines in 2 files changed: 0 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jfx/pull/1345.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1345/head:pull/1345

PR: https://git.openjdk.org/jfx/pull/1345