Using camera on iOS always prompts for microphone permission

The microphone permission should be required only when doing video recording, not when doing image capture or simply showing viewfinder frames.

That permission is automatically prompted when an audio AVCaptureDeviceInput is created and added to the capture session. The Qt plugin currently always do that, even when audio recording is not required. It should add it only when a QMediaRecorder is used and when the camera is in CaptureVideo mode.

Apps submitted to the App Store can be rejected because of this.