[Feat]: Truncated should reflect dynamic text updates

### Code of conduct

- [X] I agree to follow this project's code of conduct.

### Impacted component(s)

Truncated

### Description of the requested feature

When the text in `sp-truncated` gets changed dynamically the component should reflect that changes and update the text in the tooltip.

### Mockups or screenshots

Current behavior, see: https://studio.webcomponents.dev/edit/bvy2ZIJMtqH0wE2L1kO4/src/index.ts?p=stories

### Implementation notes or ideas

I used MutationController from @lit-labs/observers/mutation-controller.js
to reflect textContent only changes from default slot with
```
new MutationController(this, {
config: {
characterData: true,
childList: true,
subtree: true,
},
callback: () => {
this.copyText()
},
})
```

Start with the linked Studio Web Components reproduction for `sp-truncated` and inspect how its default-slot text is copied into the tooltip. Review the suggested `MutationController` approach and verify that changes to textContent, child nodes, and nested content update the tooltip; done means dynamic text is reflected reliably.

Written by the indexing model from the issue text.