This allows us to create icons with dynamic decorations drawn on top
like these:


![image](https://github.com/zed-industries/zed/assets/1714999/1d1a22df-8f90-47f2-abbd-ed7afa8fc641)

### Examples:

```rust
div()
    .child(DecoratedIcon::new(
        Icon::new(IconName::Bell).color(Color::Muted),
        IconDecoration::IndicatorDot,
    ))
    .child(
        DecoratedIcon::new(Icon::new(IconName::Bell), IconDecoration::IndicatorDot)
            .decoration_color(Color::Accent),
    )
    .child(DecoratedIcon::new(
        Icon::new(IconName::Bell).color(Color::Muted),
        IconDecoration::Strikethrough,
    ))
    .child(
        DecoratedIcon::new(Icon::new(IconName::Bell), IconDecoration::X)
            .decoration_color(Color::Error),
    )
```

Release Notes:

- N/A