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/repl/src/repl_editor.rs

@@ -85,7 +85,11 @@ pub fn run(
 
     let editor = editor.upgrade().context("editor was dropped")?;
     let selected_range = editor
-        .update(cx, |editor, cx| editor.selections.newest_adjusted(cx))
+        .update(cx, |editor, cx| {
+            editor
+                .selections
+                .newest_adjusted(&editor.display_snapshot(cx))
+        })
         .range();
     let multibuffer = editor.read(cx).buffer().clone();
     let Some(buffer) = multibuffer.read(cx).as_singleton() else {
@@ -473,7 +477,9 @@ fn language_supported(language: &Arc<Language>, cx: &mut App) -> bool {
 fn get_language(editor: WeakEntity<Editor>, cx: &mut App) -> Option<Arc<Language>> {
     editor
         .update(cx, |editor, cx| {
-            let selection = editor.selections.newest::<usize>(cx);
+            let selection = editor
+                .selections
+                .newest::<usize>(&editor.display_snapshot(cx));
             let buffer = editor.buffer().read(cx).snapshot(cx);
             buffer.language_at(selection.head()).cloned()
         })