So, uhm, 2 years ago in flutter#116429 we introduced this concept of a lookup boundary to hide certain InheritedWidgets in widget subtrees who belong to a different render tree than the InheritedWidget itself. This is for example needed for the Material widget: Buttons reach out to their Material ancestor to draw ink splashes on its associated render object. This only produces the desired effect if the button render object is a descendant of the Material render object (the two need to be in the same render tree). Overlay widgets have a similar problem. 

Lookup boundaries were specifically designed for multi view support, where a sub view would be powered by a separate and independent render tree. Ergo, widgets in the sub view shouldn't see these InheritedWidgets if they are part of the parent view. After all, it would be strange if clicking on a button in a subview draws the ink splash effect into the parent view. Unfortunately, we (and by that I really mean I) forgot to put a LayoutBoundary into the relevant multi view widgets when those were introduced in flutter#125003. This PR addresses that by wrapping the `ViewAnchor.view` child in a LookupBoundary so that its subtree (which bootstraps a separate render tree) cannot see these InheritedWidgets in the parent view.