winrt: Implement QImageEncoderControl for camera

Implement QImageEncoderControl for camera still image capture.
It provides the functions to set camera capture resolution and
get supported resolutions list.

Task-number: QTBUG-46456
Change-Id: Ideb1aa02d420be3a30d588bebf31714fa4fa6415
Reviewed-by: Oliver Wolff <oliver.wolff@theqtcompany.com>

src/plugins/winrt/qwinrtcameraservice.cpp

@@ -44,6 +44,7 @@
 #include <QtMultimedia/QCameraImageCaptureControl>
 #include <QtMultimedia/QVideoRendererControl>
 #include <QtMultimedia/QVideoDeviceSelectorControl>
+#include <QtMultimedia/QImageEncoderControl>
 
 QT_USE_NAMESPACE
 
@@ -90,6 +91,11 @@ QMediaControl *QWinRTCameraService::requestControl(const char *name)
             return d->cameraControl->imageCaptureControl();
     }
 
+    if (qstrcmp(name, QImageEncoderControl_iid) == 0) {
+        if (d->cameraControl)
+            return d->cameraControl->imageEncoderControl();
+    }
+
     return Q_NULLPTR;
 }