Extract node lifecycle, preview runtime, and Win32 input state

src/legacy_ui_node_lifecycle.h

@@ -0,0 +1,11 @@
+#pragma once
+
+class Node;
+
+namespace pp::panopainter
+{
+void legacy_ui_node_move_construct(Node& dest, Node&& src);
+void legacy_ui_node_destroy(Node& node);
+void legacy_ui_node_clone_copy(const Node& src, Node& dest);
+void legacy_ui_node_clone_children(const Node& src, Node& dest);
+}