RFR: 8343398: Add reducedData preference [v7]

[Andy Goryachev]

On Wed, 18 Dec 2024 20:52:59 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> The `reducedData` preference instructs applications to minimize internet traffic, as users might be on a metered network or a limited data plan.
>> 
>> This corresponds to the following OS settings:
>> 
>> Windows: Settings -> Network and Internet -> Ethernet/WiFi -> Metered connection
>> macOS: Settings -> Network -> Ethernet/WiFi -> Network Settings -> Low data mode
>> Ubuntu: Settings -> Network -> Wired/WiFi -> Metered connection
>> 
>> Change notifications work consistently on Windows and macOS. On my Ubuntu 24 system, the GIO `network-changed` signal is not sent when I only toggle the "metered connection" flag in network settings (and there's no signal specifically for low-data mode). The new value is only picked up when the connection changes by coming offline or going online.
>
> Michael Strauß has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - typo
>  - store the app delegate reference in MacApplication

- HelloJFXPanel does not fail anymore
- for completeness sake, ran swing/fx interop tools in the monkey tester - no problems before and after the latest changes (can't really reproduce the HelloJFXPanel use case with the MT)
- see the property events for light/dark mode and reduced data on macOS 15.1.1

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Marked as reviewed by angorya (Reviewer).

PR Review: https://git.openjdk.org/jfx/pull/1656#pullrequestreview-2512931609