feat: add diff view component

crates/editor/src/code_view.rs

@@ -287,7 +287,7 @@ impl Render for CodeViewState {
         let selection = self.selection();
 
         let gutter_chars = line_count.max(1).to_string().len().max(2);
-        let gutter_width = text_size * 0.62 * gutter_chars as f32 + text_size;
+        let gutter_width = text_size * 0.62 * (gutter_chars as f32 + 1.0);
 
         let bounds_cell: std::rc::Rc<std::cell::RefCell<Option<Bounds<Pixels>>>> =
             std::rc::Rc::new(std::cell::RefCell::new(None));
@@ -611,7 +611,7 @@ fn run_style(role: Role, selected: bool, colors: ColorTokens, ramps: Ramps) -> H
 }
 
 /// A gutter cell sized to the whole row.
-fn gutter_cell<E>(
+pub(crate) fn gutter_cell<E>(
     width: Pixels,
     height: Pixels,
     mono_font: &'static str,
@@ -637,7 +637,7 @@ where
 }
 
 /// Maps a highlight role to the theme's semantic palette.
-fn role_color(role: Role, colors: ColorTokens, ramps: Ramps) -> Hsla {
+pub(crate) fn role_color(role: Role, colors: ColorTokens, ramps: Ramps) -> Hsla {
     match role {
         Role::Text => colors.foreground,
         Role::Keyword => ramps.primary.base,