libcamera: camera: Assert pipelines complete all requests

When the camera manager calls stop on a pipeline, it is expected that
the pipeline handler guarantees all requests are returned back to the
application before the camera has stopped.

Ensure that this guarantee is met by providing an accessor on the
pipeline handler to validate that all pending requests are removed.

Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/pipeline_handler.h

@@ -80,6 +80,7 @@ public:
 
 	virtual int start(Camera *camera, const ControlList *controls) = 0;
 	virtual void stop(Camera *camera) = 0;
+	bool hasPendingRequests(const Camera *camera) const;
 
 	void queueRequest(Request *request);