Improve Order Independent Transparency example (#22781)

# Objectives

- Use a cleaner UI inspired by other examples
- Add a scene with custom material to fix #20297 

## Testing

Running the example
 ## Showcase 
<details>
<summary>Click to view showcase</summary>
<img width="872" height="732" alt="Screenshot From 2026-02-06 11-35-19"
src="https://github.com/user-attachments/assets/cc294c33-bb53-4ed4-9dce-7558f3bb8fee"
/>
<img width="872" height="732" alt="Screenshot From 2026-02-06 11-35-30"
src="https://github.com/user-attachments/assets/c2b79651-c99e-4bcc-8089-518d11631b9f"
/>
</details>

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Co-authored-by: Carter Anderson <mcanders1@gmail.com>