Reverse list of voices before returning from Speech-Dispatcher.

Since QMultiMap::values() gives voices in reverse order from the order inserted (latest first, oldest last) reverse the list before returning it to users.

Patch for Qt6 is here: https://codereview.qt-project.org/c/qt/qtspeech/+/394587 but since there won't be any more Qt 5.15 releases upstream I thought it made sense to get this in at invent.kde.org level for distros to use.

https://bugs.archlinux.org/task/73690 describes the bug this fixes. Present in both kmouth and okular at least. As well as any other qtspeech using linux application that doesn't specify which voice to use or allow the user to select it.