[jfx20] RFR: 8304359: Create release notes for JavaFX 20

[Kevin Rushforth]

Release notes for JavaFX 20, including one important change to note (the requirement of JDK 17 as the minimum needed to run JavaFX 20) and the list of enhancements and bugs fixed in this release.

Note: This PR is targeted to `jfx20`.

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Commit messages:
 - 8304359: Create release notes for JavaFX 20

Changes: https://git.openjdk.org/jfx/pull/1060/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1060&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304359
  Stats: 127 lines in 1 file changed: 127 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1060.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1060/head:pull/1060

PR: https://git.openjdk.org/jfx/pull/1060