Provide operator== for QAudioDeviceInfo. Otherwise QAudioDeviceInfo::availableDevices().indexOf and contains do not work

Title says everything. Example implementation:

bool operator==(const QAudioDeviceInfo& a, const QAudioDeviceInfo& b) {
return a.deviceName() == b.deviceName();
}

While this seems trivial, it took me a while to hunt down the error message so inclusion in Qt maybe saves wasting time from other people.