Tweak diagnostic header styling

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/editor/src/display_map/block_map.rs

@@ -72,6 +72,7 @@ pub struct BlockContext<'a> {
     pub gutter_width: f32,
     pub gutter_padding: f32,
     pub em_width: f32,
+    pub line_height: f32,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
@@ -951,6 +952,7 @@ mod tests {
                             anchor_x: 0.,
                             gutter_padding: 0.,
                             gutter_width: 0.,
+                            line_height: 0.,
                             em_width: 0.,
                         })
                         .name()

crates/editor/src/element.rs

@@ -617,6 +617,7 @@ impl EditorElement {
                     cx,
                     anchor_x,
                     gutter_padding,
+                    line_height,
                     gutter_width,
                     em_width,
                 });

crates/editor/src/items.rs

@@ -334,6 +334,8 @@ impl View for DiagnosticMessage {
                 diagnostic.message.lines().next().unwrap().to_string(),
                 theme.diagnostic_message.clone(),
             )
+            .contained()
+            .with_margin_left(theme.item_spacing)
             .boxed()
         } else {
             Empty::new().boxed()