RFR: 8365402: Bump minimum JDK version for JavaFX to JDK 24

[Kevin Rushforth]

This PR bumps the minimum version of the JDK needed to run JavaFX to JDK 24.

In order for JavaFX to be able to use more recent JDK features, we should increase the minimum version of the JDK that can run the latest JavaFX. Additionally, there is an ongoing cost to keeping JavaFX buildable and runnable on older versions of Java, and little reason to continue to do so.

This continues our current practice of setting the minimum JDK for JavaFX N to JDK N-2. JavaFX N is primarily intended for use with JDK N and we also build and test it against JDK N-1 (which is typically what we use as the boot JDK). Anything older than that, including the proposed minimum JDK N-2 (24 in this specific case), is untested.

This PR targeted to JavaFX 26, and must not be backported to any earlier version. This needs a CSR and a release note.

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Commit messages:
 - 8365402: Bump minimum JDK version for JavaFX to JDK 24

Changes: https://git.openjdk.org/jfx/pull/1883/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1883&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365402
  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/1883.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1883/head:pull/1883

PR: https://git.openjdk.org/jfx/pull/1883