Add project files.

tests/editor_headless/stubs/rlImGui.h

@@ -0,0 +1,6 @@
+#pragma once
+#include "raylib.h"
+#include "imgui.h"
+void rlImGuiSetup(bool darkTheme); void rlImGuiBegin(void); void rlImGuiEnd(void); void rlImGuiShutdown(void);
+void rlImGuiImageRenderTexture(const RenderTexture *image);
+bool rlImGuiImageButtonSize(const char *name, const Texture *image, ImVec2 size);