libcamera: camera: Handle camera objects through shared pointers

The Camera class is explicitly reference-counted to manage the lifetime
of camera objects. Replace this open-coded implementation with usage of
the std::shared_ptr<> class.

This API change prevents pipeline handlers from subclassing the Camera
class. This isn't deemed to be an issue. Mark the class final to make
this explicit.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

test/list-cameras.cpp

@@ -30,7 +30,7 @@ protected:
 	{
 		unsigned int count = 0;
 
-		for (Camera *camera : cm->cameras()) {
+		for (const std::shared_ptr<Camera> &camera : cm->cameras()) {
 			cout << "- " << camera->name() << endl;
 			count++;
 		}