Fix the display point out of range panic due to wrong coordinate space used (#62055)

Closes ZED-AKV
Closes ZED-ANB

Follow-up to https://github.com/zed-industries/zed/pull/61153

The original PR mixed up the coordinate spaces, and the newly added
methods used buffer rows (as the existing code did before that PR), but
the new code uses `FoldMap` which expects a tab row instead of the
buffer one.

Release Notes:

- Fixed a panic when selections are added by tab-expanded column