For semantic highlights, we fall back to tree-sitter highlights in the
multi buffers, as we limit the semantic tokens with the excerpt size.

Before, the fall back was also limited to the buffer excerpt, which did
not give enough highlights.

<img width="1728" height="421" alt="better_fallback"
src="https://github.com/user-attachments/assets/99517162-2d57-4369-994d-9cba8a9ac463"
/>

Release Notes:

- Fixed breadcrumb highlighting outside excerpts