Reduce display_map snapshot creation (#39354)

Re-applies https://github.com/zed-industries/zed/pull/30840

This PR re-applies the initial
[PR](https://github.com/zed-industries/zed/pull/30840). As it was closed
because it was hard to land, because of the many conflicts. This PR
re-applies the changes for it.

In several cases we were creating multiple display_map
snapshots within the same root-level function call.
Creating a display_map snapshot is quite slow, and in some
cases we were creating the snapshot multiple times.

Release Notes:

- N/A

crates/command_palette/src/command_palette.rs

@@ -698,7 +698,11 @@ mod tests {
         editor.update_in(cx, |editor, window, cx| {
             assert!(editor.focus_handle(cx).is_focused(window));
             assert_eq!(
-                editor.selections.last::<Point>(cx).range().start,
+                editor
+                    .selections
+                    .last::<Point>(&editor.display_snapshot(cx))
+                    .range()
+                    .start,
                 Point::new(2, 0)
             );
         });