git: openjdk/jfx: jfx21: 8316135: Create release notes for JavaFX 21

[Kevin Rushforth]

Changeset: 1b71f5b6
Author:    Kevin Rushforth <kcr at openjdk.org>
Date:      2023-09-18 16:38:42 +0000
URL:       https://git.openjdk.org/jfx/commit/1b71f5b63e8afa2575e0bde6d0a42ecb2e0ecde8

8316135: Create release notes for JavaFX 21

Reviewed-by: angorya
Backport-of: fa73e0d247dcadc8f80586c52ba7f92f3bb7eadb

+ doc-files/release-notes-21.md