Example Demo Implementation

[djoezeke]

Hello 👋

I'd like to propose adding a ImGuizmo_demo.cpp file to the repository — a standalone, backend-agnostic demo implementation similar to what Dear ImGui and ImPlot provide (imgui_demo.cpp, implot_demo.cpp).

Currently, the provided ImApp.h is tightly coupled to specific backends and platforms, which limits its portability and ease of integration. In many cases, it doesn't work out-of-the-box with alternative ImGui backends or on non-Windows systems.

A dedicated ImGuizmo_demo.cpp would:

• Showcase ImGuizmo features in a minimal, backend-independent way
• Make it easier for developers to integrate and test ImGuizmo in their own environments
• Align with the demo structure used by other ImGui ecosystem libraries

Let me know if this sounds reasonable — I'd be happy to help sketch out a minimal version if needed!

Thanks for your great work on this project!