Move layout metrics into theme and apply audit cleanups

crates/editor/src/diff_view.rs

@@ -13,7 +13,7 @@ use gpui::{
     point, uniform_list,
 };
 use gpui_native_core::scrollbar::{Scrollbar, ScrollbarHandle, ScrollbarVisibility};
-use gpui_native_theme::ActiveTheme as _;
+use gpui_native_theme::{ActiveTheme as _, MONO_ADVANCE_RATIO};
 use similar::{ChangeTag, TextDiff};
 
 use std::ops::Range;
@@ -399,7 +399,7 @@ fn render_row(
     let ramps = theme.ramps;
     let text_size = theme.sizes.small.text_size;
     let line_height = text_size * 1.5;
-    let char_width = text_size * 0.62;
+    let char_width = text_size * MONO_ADVANCE_RATIO;
 
     let frame = div()
         .debug_selector(move || format!("diff-row-{row_ix}"))