Make a little overlay to show diagnostics (#22486)

# Objective

`LogDiagnosticsPlugin` prints the values on the `DiagnosticStore` to the
console, which is spam-y, create an alternative that is visual

## Solution

Create `RenderAssetsOverlayPlugin` to create an UI that presents the
data for the `MaterialAllocatorDiagnosticPlugin::<StandardMaterial>` and
`MeshAllocatorDiagnosticPlugin` on a draggable and collapsable window

## Testing

Enabled it on the `many_foxes` example

## Showcase

<img width="1920" height="1036" alt="image"
src="https://github.com/user-attachments/assets/f44b663b-cf77-4c18-8df8-48c9d2ec7fdd"
/>

<img width="1920" height="1036" alt="image"
src="https://github.com/user-attachments/assets/6d807092-bde3-4aef-af81-b6ac0d32ea1c"
/>

Author: hukasu