[API design] Fix bogus AbsListView.Adapter / RawAdapter #1116
Description
I have no idea how this could occur from the beginning, but Android.Widget.AbsListView has bogus property definition "Adapter" which (1) has fake mapping to getAdapter() which DOES NOT EXIST (there is NO IMPLEMENTATION), and (2) invalidates all the relevant effort to make correct mapping to Java getAdapter and setAdapter in the derived classes in third party Java libraries.
Having Adapter overridable is all wrong. It must be either completely vanished or made non-virtual, just to become a utility property that only delegates to RawAdapter.
This was why #1032 was failing.
To fix this issue -
(1) add [Obsolete ("Do not override this property. It was design mistake. Override RawAdapter instead.")]. We will have to eliminate this once
(2) add another utility property (something like TypedAdapter) which is not Java.Lang.Object unlike RawAdapter, so that we can later remove Adapter property. The implementation is just a typed delegate to RawAdapter.