RFR: 8299681: Change JavaFX release version to 21

[Kevin Rushforth]

Bump the version number of JavaFX to 21. I will integrate this to `master` as part of forking the `jfx20` stabilization branch, which is scheduled for Thursday, January 12, 2023 at 16:00 UTC.

-------------

Commit messages:
 - 8299681: Change JavaFX release version to 21

Changes: https://git.openjdk.org/jfx/pull/990/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=990&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299681
  Stats: 5 lines in 3 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/990.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/990/head:pull/990

PR: https://git.openjdk.org/jfx/pull/990