Use outline (#29687)

## Before

![Screenshot 2025-04-30 at 10 56
36 AM](https://github.com/user-attachments/assets/3a435f4c-ad45-4f26-a847-2d5c9d03648e)

## After

![Screenshot 2025-04-30 at 10 55
27 AM](https://github.com/user-attachments/assets/cc3a8144-b6fe-4a15-8a47-b2487ce4f66e)

Release Notes:

- Context picker and `@`-mentions now work with very large files.
50f705e779Richard Feldman committed on 4/30/2025, 6:00:00 PM· committed by GitHubparent8173534
8 files changedLine totals unavailable