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/editor/src/tasks.rs

@@ -14,7 +14,7 @@ impl Editor {
             return Task::ready(None);
         };
         let (selection, buffer, editor_snapshot) = {
-            let selection = self.selections.newest_adjusted(cx);
+            let selection = self.selections.newest_adjusted(&self.display_snapshot(cx));
             let Some((buffer, _)) = self
                 .buffer()
                 .read(cx)