fcitx-qt5 1.2.7 for Qt6 support

[Weng Xuetian]

Hi all,
Though we don't have any active development in fcitx4, we still rarely
provide some important updates.

This release is mainly to add Qt6 support to the build system, despite
that the package name is a little bit confusing. It only provides the
Qt6 im module (No library). Qt5 and Qt6 support can be built at the
same time. Simply pass "-DENABLE_QT6=On" then it will build the Qt6
plugin. "-DCMAKE_INSTALL_QT6PLUGINDIR" can be used to set the plugin
installation path.

Thanks,
Xuetian