Use recently stabilized intra-doc links

See RFC: https://github.com/rust-lang/rfcs/blob/master/text/1946-intra-rustdoc-links.md

native/src/widget/pane_grid/split.rs

@@ -1,5 +1,5 @@
 /// A divider that splits a region in a [`PaneGrid`] into two different panes.
 ///
-/// [`PaneGrid`]: struct.PaneGrid.html
+/// [`PaneGrid`]: crate::widget::PaneGrid
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct Split(pub(super) usize);