[jfx21u] RFR: 8314484: Update Gradle to 8.4

[Ambarish Rapte]

Clean backport to jfx21.
Verified a build locally on macOS.

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Commit messages:
 - 8318115: Webkit build fails after gradle 8.4
 - 8314484: Update Gradle to 8.4
 - 8314486: JavaFX build uses deprecated features that will be removed in gradle 8

Changes: https://git.openjdk.org/jfx21u/pull/22/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx21u&pr=22&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314484
  Stats: 318 lines in 7 files changed: 41 ins; 236 del; 41 mod
  Patch: https://git.openjdk.org/jfx21u/pull/22.diff
  Fetch: git fetch https://git.openjdk.org/jfx21u.git pull/22/head:pull/22

PR: https://git.openjdk.org/jfx21u/pull/22