Add new terminal in new window to top-level Terminal window

This:

<img width="371" height="373" alt="Image" src="https://github.com/user-attachments/assets/38420f4a-95eb-4219-80f7-dccc3db424b8" />

Should get similar treatment as in https://github.com/microsoft/vscode/pull/259422

<img width="744" height="1038" alt="Image" src="https://github.com/user-attachments/assets/5fbe06fe-6e32-4c2b-985c-93b94775415b" />