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/collab_ui/src/channel_view.rs

@@ -287,9 +287,12 @@ impl ChannelView {
     }
 
     fn copy_link(&mut self, _: &CopyLink, window: &mut Window, cx: &mut Context<Self>) {
-        let position = self
-            .editor
-            .update(cx, |editor, cx| editor.selections.newest_display(cx).start);
+        let position = self.editor.update(cx, |editor, cx| {
+            editor
+                .selections
+                .newest_display(&editor.display_snapshot(cx))
+                .start
+        });
         self.copy_link_for_position(position, window, cx)
     }