Reworked Scrollable to account for lack of widget order guarantees.

Fixed thumb "snapping" bug on scrollable when cursor is out of bounds.

src/widget.rs

@@ -99,8 +99,7 @@ pub mod radio {
 pub mod scrollable {
     //! Navigate an endless amount of content with a scrollbar.
     pub use iced_native::widget::scrollable::{
-        snap_to, style::Scrollbar, style::Scroller, Direction, Horizontal, Id,
-        StyleSheet,
+        snap_to, style::Scrollbar, style::Scroller, Id, Properties, StyleSheet,
     };
 
     /// A widget that can vertically display an infinite amount of content