Update navigation_and_routing sample to go_router (#2067)

This is a new PR to update the navigation_and_routing sample to the
latest version of go_router. It is a based on
https://github.com/flutter/samples/pull/1437

---------

Co-authored-by: Brett Morgan <brettmorgan@google.com>

navigation_and_routing/lib/src/data/library.dart

@@ -51,6 +51,10 @@ class Library {
     allBooks.add(book);
   }
 
+  Book getBook(String id) {
+    return allBooks[int.parse(id)];
+  }
+
   List<Book> get popularBooks => [
         ...allBooks.where((book) => book.isPopular),
       ];