libcamera: pipeline: Utilise shared MediaDevice pointers

Adapt the PipelineHandler::acquireMediaDevice() support function to
return a shared pointer instead of the underlying raw pointer.

Propagate this update to all pipeline handlers that use the MediaDevice
and store a std::shared_ptr<MediaDevice> accordingly.

This is required to support media devices that are potentially shared
among multiple pipeline handlers, like a dewarper implemented as v4l2
m2m device.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Isaac Scott <isaac.scott@ideasonboard.com>

test/libtest/buffer_source.cpp

@@ -52,7 +52,8 @@ int BufferSource::allocate(const StreamConfiguration &config)
 		return TestSkip;
 	}
 
-	std::unique_ptr<V4L2VideoDevice> video = V4L2VideoDevice::fromEntityName(media_.get(), videoDeviceName);
+	std::unique_ptr<V4L2VideoDevice> video = V4L2VideoDevice::fromEntityName(media_.get(),
+										 videoDeviceName);
 	if (!video) {
 		std::cout << "Failed to get video device from entity "
 			  << videoDeviceName << std::endl;