Introduce a visible_bounds parameter to Element::paint

We're not using this yet but this will be useful to avoid rendering
unnecessary portions of text.

zed/src/editor/element.rs

@@ -559,6 +559,7 @@ impl Element for EditorElement {
     fn paint(
         &mut self,
         bounds: RectF,
+        _: RectF,
         layout: &mut Self::LayoutState,
         cx: &mut PaintContext,
     ) -> Self::PaintState {