New Rule: `no-unscoped-nesting-selector`

### Rule details

Disallow the nesting selector (`&`) in a context with no scoping root

### What type of rule is this?

Warns about a potential problem

### Example code

```css
/* ✗ no enclosing style rule: per css-nesting, `&` here "represents the same
elements as :scope", so this silently styles the root element */
& {
color: red;
}

/* ✓ the enclosing style rule is the scoping root */
a {
& span {
color: red;
}
}
```

### Prior Art

https://stylelint.io/user-guide/rules/nesting-selector-no-missing-scoping-root

### Participation

- [x] I am willing to submit a pull request to implement this rule.

### AI acknowledgment

- [x] I did not use AI to generate this issue report.
- [ ] (If the above is not checked) I have reviewed the AI-generated content before submitting.

### Additional comments

_No response_