multi_buffer: Reduce RefCell::borrow_mut calls to the bare minimum (#40522)

Release Notes:

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

crates/editor/src/editor.rs

@@ -6887,7 +6887,8 @@ impl Editor {
                                 continue;
                             }
 
-                            let range = Anchor::range_in_buffer(excerpt_id, buffer_id, start..end);
+                            let range =
+                                Anchor::range_in_buffer(excerpt_id, buffer_id, *start..*end);
                             if highlight.kind == lsp::DocumentHighlightKind::WRITE {
                                 write_ranges.push(range);
                             } else {

crates/editor/src/element.rs

@@ -7465,7 +7465,7 @@ impl EditorElement {
                         let clipped_start = range.start.max(&buffer_range.start, buffer);
                         let clipped_end = range.end.min(&buffer_range.end, buffer);
                         let range = buffer_snapshot
-                            .anchor_range_in_excerpt(excerpt_id, clipped_start..clipped_end)?;
+                            .anchor_range_in_excerpt(excerpt_id, *clipped_start..*clipped_end)?;
                         let start = range.start.to_display_point(display_snapshot);
                         let end = range.end.to_display_point(display_snapshot);
                         let selection_layout = SelectionLayout {