Scope the Focusable item for AutoFocusDirective so that any node in the hierarchy isn't mistakenly focused.

PiperOrigin-RevId: 204985250

Author: TedSander

lib/focus/focus.dart

@@ -137,7 +137,7 @@ class AutoFocusDirective extends RootFocusable implements OnInit, OnDestroy {
   AutoFocusDirective(
       HtmlElement node,
       this._domService,
-      @Optional() this._focusable,
+      @Self() @Optional() this._focusable,
       @Optional() this._modal,
       @Optional() this._popupRef)
       : super(node);