This changes the behavior of requestFocus when it is called on a FocusNode that does not yet have a parent, so that it defers requesting focus until it receives a parent. Before this change, calling requestFocus before it had a parent was a no-op.

This allows scenarios where a widget is newly added and wishes to immediately request the focus. Previously, it was very hard to make that work because requesting focus before the widget's focus node had a parent was ignored, so the developer had to wait until two frames later to request focus (one for the widget's node to be added to the focus tree, and one to request the focus).

Now, in order to have a widget be focused when initially added, you just need to call requestFocus on its node when you create it, and as soon as it is added, it will automatically request focus.

This is different from the autofocus attribute on the Focus widget, because it unconditionally requests focus when added (autofocus will only request focus if nothing else in the scope has focus).