tree-wide: fix rustdoc warnings, add some links

crates/syntax/src/ast/node_ext.rs

@@ -197,12 +197,12 @@ pub enum AttrKind {
 }
 
 impl AttrKind {
-    /// Returns `true` if the attr_kind is [`Inner`].
+    /// Returns `true` if the attr_kind is [`Inner`](Self::Inner).
     pub fn is_inner(&self) -> bool {
         matches!(self, Self::Inner)
     }
 
-    /// Returns `true` if the attr_kind is [`Outer`].
+    /// Returns `true` if the attr_kind is [`Outer`](Self::Outer).
     pub fn is_outer(&self) -> bool {
         matches!(self, Self::Outer)
     }