RFR: 8289835: Change JavaFX release version to 20

Fri Jul 8 19:29:18 UTC 2022

Bump the version number of JavaFX to 20. I will integrate this to `master` as part of forking the `jfx19` stabilization branch, which is scheduled for Thursday, July 14, 2022 at 16:00 UTC.

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Commit messages:
 - 8289835: Change JavaFX release version to 20

Changes: https://git.openjdk.org/jfx/pull/820/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=820&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289835
  Stats: 5 lines in 3 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/820.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/820/head:pull/820

PR: https://git.openjdk.org/jfx/pull/820