Graphics: Rework RenderTargets

- RenderTarget have been moved to the Graphics module and are now lightweight objects between the target of rendering (swapchain or texture)
- RenderTexture no longer require a blit between the framegraph texture and the target texture (the target texture is now directly rendered onto using a new feature of the framegraph)
- ForwardFramePipeline viewers are now properly ordered by render order

examples/PhysicsDemo/main.cpp

@@ -96,7 +96,7 @@ int main(int argc, char* argv[])
 	entt::handle viewer = world.CreateEntity();
 	{
 		viewer.emplace<Nz::NodeComponent>();
-		auto& cameraComponent = viewer.emplace<Nz::CameraComponent>(&windowSwapchain);
+		auto& cameraComponent = viewer.emplace<Nz::CameraComponent>(std::make_shared<Nz::RenderWindow>(windowSwapchain));
 		cameraComponent.UpdateRenderMask(1);
 		cameraComponent.UpdateClearColor(Nz::Color(0.5f, 0.5f, 0.5f));
 	}