- add `Rect::is_empty()` that checks whether either height or width == 0 - refactored `Rect` into layout/rect.rs from layout.rs. No public API change as the module is private and the type is re-exported under the `layout` module.
- add `Rect::is_empty()` that checks whether either height or width == 0 - refactored `Rect` into layout/rect.rs from layout.rs. No public API change as the module is private and the type is re-exported under the `layout` module.