RFR: 8343398: Add reducedData preference [v2]

[Michael Strauß]

> 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:

  javadoc change

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/1656/files
  - new: https://git.openjdk.org/jfx/pull/1656/files/0245c2e4..5c2e255f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1656&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1656&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1656.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1656/head:pull/1656

PR: https://git.openjdk.org/jfx/pull/1656