diagnostics: Keep diagnostic excerpt ranges properly ordered (#42298)

Fixes ZED-2CQ

We were doing the binary search by buffer points, but due to await
points within this function we could end up mixing points of differing
buffer versions.

Release Notes:

- N/A *or* Added/Fixed/Improved ...
b7d4d1791aLukas Wirth committed on 11/9/2025, 10:55:56 AM· committed by GitHubparent81d38d9
6 files changedLine totals unavailable