layout_2020: Add an optional box size parameter to ReplacedContent::used_size_as_if_inline_element

This allow us to specify the used size when calculating size of
replaced content.

components/layout_2020/positioned.rs

@@ -439,6 +439,7 @@ impl HoistedAbsolutelyPositionedBox {
                 let used_size = replaced.contents.used_size_as_if_inline_element(
                     &containing_block.into(),
                     &replaced.style,
+                    None,
                     &pbm,
                 );
                 Vec2 {