QSoundEffect has generic PulseAudio application name

When creating a QSoundEffect the resulting PulseAudio stream only has a very generic application name (QtPulseAudio:<pid>) property. It would be better to have a proper name there. QGuiApplication::applicationDisplayName() looks like a natural candidate to me.

To do this one needs to set the PA_PROP_APPLICATION_NAME property: https://freedesktop.org/software/pulseaudio/doxygen/proplist_8h.html#ab94d533153744b934780ce627ef3e74c