chore(docs-app): ensure ToC links contain the path

Without the path the link is always pointing to the
root page, rather than the current page, which means
that copying the link address or opening the page in
a new tab is broken.

Closes #16608

docs/app/src/directives.js

@@ -91,13 +91,16 @@ directivesModule
 .component('tocTree', {
   template: '<ul>' +
       '<li ng-repeat="item in $ctrl.items">' +
-        '<a ng-href="#{{item.fragment}}">{{item.title}}</a>' +
+        '<a ng-href="{{ $ctrl.path }}#{{item.fragment}}">{{item.title}}</a>' +
         '<toc-tree ng-if="::item.children.length > 0" items="item.children"></toc-tree>' +
       '</li>' +
     '</ul>',
   bindings: {
     items: '<'
-  }
+  },
+  controller: ['$location', function($location) {
+    this.path = $location.path().replace(/^\/?(.+?)(\/index)?\/?$/, '$1');
+  }]
 })
 .directive('tocContainer', function() {
   return {