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/debugger_ui/src/debugger_ui.rs

@@ -341,8 +341,10 @@ pub fn init(cx: &mut App) {
                                 maybe!({
                                     let (buffer, position, _) = editor
                                         .update(cx, |editor, cx| {
-                                            let cursor_point: language::Point =
-                                                editor.selections.newest(cx).head();
+                                            let cursor_point: language::Point = editor
+                                                .selections
+                                                .newest(&editor.display_snapshot(cx))
+                                                .head();
 
                                             editor
                                                 .buffer()
@@ -392,7 +394,10 @@ pub fn init(cx: &mut App) {
                                 let text = editor
                                     .update(cx, |editor, cx| {
                                         editor.text_for_range(
-                                            editor.selections.newest(cx).range(),
+                                            editor
+                                                .selections
+                                                .newest(&editor.display_snapshot(cx))
+                                                .range(),
                                             &mut None,
                                             window,
                                             cx,