editor: Shrink DisplayMapSnapshot from 824 to 256 bytes (#39568)

We have unnecessary clones for the fields here as most of the snapshots
contain the others hierarchically.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/editor/src/test/editor_test_context.rs

@@ -504,7 +504,7 @@ impl EditorTestContext {
                 .map(|h| h.1.clone())
                 .unwrap_or_default()
                 .iter()
-                .map(|range| range.to_offset(&snapshot.buffer_snapshot))
+                .map(|range| range.to_offset(&snapshot.buffer_snapshot()))
                 .collect()
         });
         assert_set_eq!(actual_ranges, expected_ranges);
@@ -519,7 +519,7 @@ impl EditorTestContext {
             .map(|ranges| ranges.as_ref().clone().1)
             .unwrap_or_default()
             .into_iter()
-            .map(|range| range.to_offset(&snapshot.buffer_snapshot))
+            .map(|range| range.to_offset(&snapshot.buffer_snapshot()))
             .collect();
         assert_set_eq!(actual_ranges, expected_ranges);
     }
@@ -579,7 +579,7 @@ pub fn assert_state_with_diff(
 ) {
     let (snapshot, selections) = editor.update_in(cx, |editor, window, cx| {
         (
-            editor.snapshot(window, cx).buffer_snapshot.clone(),
+            editor.snapshot(window, cx).buffer_snapshot().clone(),
             editor.selections.ranges::<usize>(cx),
         )
     });