Add is_tab field to chunks

Co-authored-by: Antonio Scandurra <antonio@zed.dev>

crates/editor/src/display_map/block_map.rs

@@ -833,10 +833,7 @@ impl<'a> Iterator for BlockChunks<'a> {
 
             return Some(Chunk {
                 text: unsafe { std::str::from_utf8_unchecked(&NEWLINES[..line_count as usize]) },
-                syntax_highlight_id: None,
-                highlight_style: None,
-                diagnostic_severity: None,
-                is_unnecessary: false,
+                ..Default::default()
             });
         }