RFR: 8343398: Add reducedData preference [v3]

[Michael Strauß]

On Wed, 4 Dec 2024 15:55:20 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 one additional commit since the last revision:
> 
>   refactor macOS PlatformSupport

This PR also includes a small refactor of the GTK and macOS `PlatformSupport` classes.

The previous implementations had some parts of the change notification mechanism implemented outside of `PlatformSupport` in their respective `GlassApplication` class. The refactor moves this into `PlatformSupport`, which centralizes all aspects related to platform preference change detection.

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PR Comment: https://git.openjdk.org/jfx/pull/1656#issuecomment-2517866653