Use item_name instead of pretty printing

Pretty printing would add a `r#` prefix to raw identifiers, which was
not correct. In general I think this change makes sense -
pretty-printing is for showing to the *user*, `item_name` is suitable to
pass to resolve.

src/test/rustdoc/intra-doc/raw-ident-self.rs

@@ -0,0 +1,13 @@
+#![deny(broken_intra_doc_links)]
+pub mod r#impl {
+    pub struct S;
+
+    impl S {
+        /// See [Self::b].
+        // @has raw_ident_self/impl/struct.S.html
+        // @has - '//a[@href="../../raw_ident_self/impl/struct.S.html#method.b"]' 'Self::b'
+        pub fn a() {}
+
+        pub fn b() {}
+    }
+}