RFR: 8343196: Add build property to identify experimental builds of JavaFX

[Ambarish Rapte]

Introduce a new build property `jfx.experimental.release.suffix` to be used for the early access builds of an under development feature in JavaFX.
This property would be set to a value ONLY in a branch specific to an experiment in [jfx-sandbox](https://github.com/openjdk/jfx-sandbox) repo.
For example:
For the metal branch in jfx-sandbox repo, it would be set to `-metal`.  The javafx.version for the early access build generated from that branch would be `24-metal`.

And it would always be empty for master branch in both main jfx repo and in jfx-sandbox repo.
This change has no effect on a regular developer build from master branch.

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Commit messages:
 - 8343196: Add build property to identify experimental builds of JavaFX

Changes: https://git.openjdk.org/jfx/pull/1637/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1637&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343196
  Stats: 15 lines in 2 files changed: 14 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1637.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1637/head:pull/1637

PR: https://git.openjdk.org/jfx/pull/1637