RFR: 8290530: Bump minimum JDK version for JavaFX to JDK 17 [v5]

[Johan Vos]

On Wed, 27 Jul 2022 18:59:00 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> This PR bumps the minimum JDK version needed to build and run JavaFX to JDK 17, starting with JavaFX 20.
>> 
>> As discussed in [this thread](https://mail.openjdk.org/pipermail/openjfx-dev/2022-July/034874.html) on the `openjfx-dev` mailing list, this means that we can start using language features and APIs available from JDK 12 through 17. However, this is not an open invitation to globally refactor data classes into records, or change all multi-line Strings into text blocks. Rather we will be able to start using recent JDK capabilities in new code where it makes sense to do so.
>> 
>> The changes are as follows:
>> 
>> 1. Added a new `jfx.jdk.target.version` property in `build.properties` to define the minimum JDK version, and set it to 17.
>> 2. Bumped the minimum version of the boot JDK to 17 and the minimum version of gradle to 7.3.
>> 3. Use the recent gradle feature to implement the minimum JDK version using `--release NN` instead of `-source NN -target NN` where possible (everywhere except when building the `javafx.swing` module and the system tests).
>> 4. Update `CONTRIBUTING.md` to say that JDK 17 is the minimum.
>> 
>> Because this change has behavioral compatibility impact, it will need a CSR and a release note.
>
> Kevin Rushforth has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix typo: unsupoprted -> unsupported

Marked as reviewed by jvos (Reviewer).

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PR: https://git.openjdk.org/jfx/pull/850