Extract menu, stylus, and canvas draw helpers

src/platform_windows/windows_stylus_input.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include <windows.h>
+
+namespace pp::platform::windows {
+
+void initialize_stylus_input();
+void update_stylus_state(float dt);
+void note_wintab_packet();
+void handle_pointer_update_message(WPARAM wp);
+
+}