Right align thicker scrollbar in completion popup

- Aligns the scollbar to the right edge of the popup rather than at
  a margin of one.
- Changes the scrollbar block character to be thicker.

helix-term/src/ui/menu.rs

@@ -320,10 +320,8 @@ impl<T: Item + 'static> Component for Menu<T> {
             let is_marked = i >= scroll_line && i < scroll_line + scroll_height;
 
             if !fits && is_marked {
-                let cell = &mut surface[(area.x + area.width - 2, area.y + i as u16)];
-                cell.set_symbol("▐");
-                // cell.set_style(selected);
-                // cell.set_style(if is_marked { selected } else { style });
+                let cell = &mut surface[(area.x + area.width - 1, area.y + i as u16)];
+                cell.set_symbol("🮊"); // right three quarters block
             }
         }
     }