languages: Include namespace in the outline for C++ (#45794)

Before: 

<img width="389" height="147" alt="image"
src="https://github.com/user-attachments/assets/5412bde6-2f1b-4bb4-a06f-111724597372"
/>

After:
<img width="404" height="139" alt="image"
src="https://github.com/user-attachments/assets/8f906245-4c6e-4cf0-bb32-1b47048f46c0"
/>


Release Notes:

- Include namespace symbol in the outline view for C++.
6625997e0fHaojian Wu committed on 1/5/2026, 9:13:08 PM· committed by GitHubparent0e5b6a5
1 file changedLine totals unavailable