* Use default `render` method in the `Frame` view.
* Rename `Views.attach` to `Views.insert`.
* Add `Views.all` to retrieve all subviews.
* Add `Views.detach` to detach all subviews.
* Detect whether views are going to be reused in `View.set` and `detach` them instead of calling `dispose`.
see #21390.
git-svn-id: https://develop.svn.wordpress.org/trunk@22662 602fd350-edb4-49c9-b593-d223f7449a82