Interface to set QAudioSource/QAudioSink stream name

Qt Multimedia does not have an interface to set the stream name via QAudioSource/QAudioSink. Looking at the pulseaudio plugin code for example, the variable m_streamName is never set and the code defaults to an auto generated name.

I believe the comment made on the previous bug report by Lars Knoll is incorrect in that GStreamer/FFmpeg is not actually used by the QAudioSource/Sink classes, instead they seem to have their own internal ALSA/Pulse plugins separate from the rest of the multimedia module, so instead of "the pulse backend is untested" it appears to be the one that is actually used the most on modern distros.