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

include/Nazara/Graphics/FramePass.hpp

@@ -97,8 +97,8 @@ namespace Nz
 
 			struct Output
 			{
-				std::size_t attachmentId;
 				std::optional<Color> clearColor;
+				std::size_t attachmentId;
 			};
 
 		private: