RFR: 8340378: [XWayland] FXCanvas apps and tests crash on Ubuntu 24.04

[Kevin Rushforth]

On Fri, 12 Sep 2025 08:32:38 GMT, Jayathirth D V <jdv at openjdk.org> wrote:

> As mentioned in recent PR : https://github.com/openjdk/jfx/pull/1890#issue-3401783091, we need to set environment variable GDK_BACKEND=x11 for running HelloFXCanvas also.
> 
> There is no correct way of setting environment variable through Java code/Netbeans project files. So we are capturing this additional step for Linux in README.txt.

LGTM

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Marked as reviewed by kcr (Lead).

PR Review: https://git.openjdk.org/jfx/pull/1898#pullrequestreview-3216991118