Support cursor in decoration attachments (before / after)

I’m working on a VS Code extension that uses `before`/`after` decoration attachments to show small inline indicators next to CSS declarations.

I ran into a limitation with the current API: there doesn’t seem to be a way to set the cursor for an attachment itself.

For example, I’d like to be able to do something like:

```ts
after: {
contentIconPath: warningIcon,
cursor: 'pointer'
}
```

This would be useful for extensions that render inline icons or indicators that are interactive, where changing the cursor only when it is over the attachment would make it clear that the indicator can be interacted with.

Would it be possible to support a `cursor` property in `ThemableDecorationAttachmentRenderOptions`?

Something along the lines of:

```ts
interface ThemableDecorationAttachmentRenderOptions {
// ...
cursor?: string;
}
```

This would also avoid extensions having to rely on CSS injection or other workarounds to achieve this.