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/src/tests/editor_tests.rs

@@ -877,7 +877,7 @@ async fn test_collaborating_with_renames(cx_a: &mut TestAppContext, cx_b: &mut T
             6..9
         );
         rename.editor.update(cx, |rename_editor, cx| {
-            let rename_selection = rename_editor.selections.newest::<usize>(cx);
+            let rename_selection = rename_editor.selections.newest::<usize>(&rename_editor.display_snapshot(cx));
             assert_eq!(
                 rename_selection.range(),
                 0..3,
@@ -924,7 +924,7 @@ async fn test_collaborating_with_renames(cx_a: &mut TestAppContext, cx_b: &mut T
         let lsp_rename_end = rename.range.end.to_offset(&buffer);
         assert_eq!(lsp_rename_start..lsp_rename_end, 6..9);
         rename.editor.update(cx, |rename_editor, cx| {
-            let rename_selection = rename_editor.selections.newest::<usize>(cx);
+            let rename_selection = rename_editor.selections.newest::<usize>(&rename_editor.display_snapshot(cx));
             assert_eq!(
                 rename_selection.range(),
                 1..2,