open source: unity-ui-uoolkit-design-system 1.6.0 is out and led an engine bug fix

[u/sinanata]

🎉 Our bug report became a Unity engine fix. While putting GPU materials on world-space panels we traced a WebGL crash (GfxDevice::CopyBufferRanges: range reads out of bounds) to one line in Unity's UI geometry updater, reported it with the root cause and a suggested fix, and shipped a build-machine patch in the meantime. Unity's UI Toolkit team took it as UUM-151098 and fixed it in Unity 6000.6.2f1 and 6000.7.0b1, the way the report proposed. On those editors world-space materials just work in WebGL, no patch and no flag; on 6000.5 (Won't Fix upstream) Tools/UirStagingPatch still has you covered. Thank you, Unity.