Closes #38576

In case of inline element rendering, we can have multiple text runs on
the same display row. There was a bug in
https://github.com/zed-industries/zed/pull/37165 which doesn't consider
this multiple text runs case. This PR fixes that and adds a test for it.

Before:

<img width="600" alt="image"
src="https://github.com/user-attachments/assets/3bdf5f14-988b-45dc-bc8e-c5d61ab35a93"
/>

After:

<img width="600" alt="image"
src="https://github.com/user-attachments/assets/0e1a45ff-c521-4994-b259-3a054d89c4df"
/>

Release Notes:

- Fixed an issue where text could be incorrectly highlighted during
search when a line contained an inline color preview.