Add support for 4-digit ARGB short hex in QColor

ARGB hex values can be represented in 4-digit and 8-digit hex codes, similar to how RGB can be 3- and 6-digit. Support for this started as early as 2016 from chrome and firefox. I checked the dev branch documentation for Qt 6.10.0 which also did not include this feature.

For my instance, KDE's Kate color picker plugin cannot currently detect text that is 4 digit hex codes and convert using https://doc.qt.io/qt-6/qcolor.html#fromString

Thanks, sorry if this is the wrong component listing.