Long live Qt for HarmonyOS!

With [change 733351 in Qt Gerrit][1] now merged into the dev branch of qtbase, along with several other changes merged into the qt5 dev branch (see [the harmonyos_upstream topic][2]), qtbase dev now supports building on HarmonyOS 6.0.0 (API Level 20).

If you are interested in building qtbase for HarmonyOS, please refer to the [Qt Wiki page][3].

[1]: https://codereview.qt-project.org/c/qt/qtbase/+/733351 [2]: https://codereview.qt-project.org/q/topic:%22harmonyos_upstr... [3]: https://wiki.qt.io/Building_Qt6_for_HarmonyOS