RFR: 8378383: Create release notes for JavaFX 26

[Kevin Rushforth]

This PR adds the release notes for the JavaFX 26 release. This will first go into master, and then be backported to the jfx26 branch so it will be available in that branch when JavaFX 26 is published (and from there also synced into the jfx26u repo).

The following filter was used to produce the list of issues fixed in JavaFX 26:

https://bugs.openjdk.org/issues/?filter=49209

Additionally, we had three issues with a `release-note=yes` label, which are included in the list of important changes, etc.

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Commit messages:
 - 8378383: Create release notes for JavaFX 26

Changes: https://git.openjdk.org/jfx/pull/2090/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=2090&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378383
  Stats: 167 lines in 1 file changed: 167 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/2090.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2090/head:pull/2090

PR: https://git.openjdk.org/jfx/pull/2090