libcamera: pipeline_handler: Return unique_ptr from createInstance

Avoid naked pointer with memory allocation by returning a unique_ptr
from PipelineHandlerFactory::createInstance(), in order to increase
memory allocation safety.

This allows iterating over factories in the CameraManager and unit tests
using const pointers.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Xavier Roumegue <xavier.roumegue@oss.nxp.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/internal/pipeline_handler.h

@@ -113,7 +113,8 @@ public:
 private:
 	static void registerType(PipelineHandlerFactory *factory);
 
-	virtual PipelineHandler *createInstance(CameraManager *manager) const = 0;
+	virtual std::unique_ptr<PipelineHandler>
+	createInstance(CameraManager *manager) const = 0;
 
 	std::string name_;
 };
@@ -125,9 +126,10 @@ public:									\
 	handler##Factory() : PipelineHandlerFactory(#handler) {}	\
 									\
 private:								\
-	PipelineHandler *createInstance(CameraManager *manager) const	\
+	std::unique_ptr<PipelineHandler>				\
+	createInstance(CameraManager *manager) const			\
 	{								\
-		return new handler(manager);				\
+		return std::make_unique<handler>(manager);		\
 	}								\
 };									\
 static handler##Factory global_##handler##Factory;