refactor layout.h into single file per Node* classes

engine/node_canvas.h

@@ -0,0 +1,21 @@
+#pragma once
+#include "node.h"
+#include "canvas.h"
+
+class NodeCanvas : public Node
+{
+public:
+    std::string data_path;
+    std::unique_ptr<ui::Canvas> m_canvas;
+    ui::Brush m_brush;
+    Sampler m_sampler;
+    ui::Plane m_face_plane;
+    ui::LineSegment m_line;
+    virtual Node* clone_instantiate() const override;
+    virtual void init() override;
+    virtual void restore_context() override;
+    virtual void clear_context() override;
+    virtual void draw() override;
+    virtual void handle_resize(glm::vec2 old_size, glm::vec2 new_size) override;
+    virtual kEventResult handle_event(Event* e) override;
+};