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/PhysicallyBasedRendering/main.cpp

@@ -61,7 +61,7 @@ int main(int argc, char* argv[])
 
 	Nz::Vector2ui windowSize = window.GetSize();
 
-	Nz::Camera camera(&windowSwapchain);
+	Nz::Camera camera(std::make_shared<Nz::RenderWindow>(windowSwapchain));
 	//camera.UpdateClearColor(Nz::Color::Gray);
 
 	Nz::ViewerInstance& viewerInstance = camera.GetViewerInstance();