C# Class SIL.FieldWorks.Common.RootSites.AccessibilityWrapper

This class implements the DotNet Acessibility interface by wrapping the COM IAccessible interface implemented by the root box. It is uncomfortably similar to COMInterfaces.AccessibleObjectFromIAccessible, but was developed independently since we (JohnT and Dan) didn't find AccessibleObjectFromIAccessible until later. The most important difference is that this version stores the root site as well as its AccessibleRootObject. This handles the problem that DotNet apparently only asks any one object to CreateAccessibilityInstance() once; then it caches the result. So if we return null, or make an AccessibleObjectFromIAccessible that has a null IAccessible, it will never work later when the root box has been made and the IAccessible is available. (In fact, it crashes, because AccessibleObjectFromIAccessible is not coded to handle a null IAccessible.) This class, whenever it needs the IAccessble, checks whether it is null. If so, it checks the root site to see whether it is now possible to get a proper AccessibleRootObject, and if so starts using it. If not, it answers something safe and neutral. It's possible that we could refactor to share some code between the two classes, for example, give AccessibleObjectFromIAccessible a virtual method to get the IAccessible (and always use it), then this class might only need to override that method to try getting the IAcessible from the rootsite if it doesn't already have one. However, we'd have to merge into AccessibleObjectFromIAccessible all the code from here that handles IAccessible being null. Another possible way to remove the duplication is just to delete AccessibleObjectFromIAccessible, since it doesn't seem to be used and was possibly just an unsuccessful attempt at what this class seems to do successfully.