RFR: 8248317: Change JavaFX release version to 16

[Kevin Rushforth]

Bump the version number of JavaFX to 16. I will integrate this immediately after forking the `jfx15` stabilization
branch.

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Commit messages:
 - 8248317: Change JavaFX release version to 16

Changes: https://git.openjdk.java.net/jfx/pull/260/files
 Webrev: https://webrevs.openjdk.java.net/jfx/260/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248317
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/260.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/260/head:pull/260

PR: https://git.openjdk.java.net/jfx/pull/260