Make autoscroll optional when highlighting editor rows (#11950)

Previously, when highlighting editor rows with a color, we always
auto-scrolled to the first highlighted row. This was useful in contexts
like go-to-line and the outline view. We had an explicit special case
for git diff highlights. Now, part of the `highlight_rows` API, you
specify whether or not you want the autoscroll behavior. This is needed
because we want to highlight rows in the assistant panel, and we don't
want the autoscroll.

Release Notes:

- N/A