SoftDebuggerAdaptor.GetValueType() can return System.Type (not always TypeMirror)
SoftDebuggerAdaptor.GetValueType() can return System.Type (not always TypeMirror)

Properly handle this case when getting a hoisted @this reference

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/901162/

mono/debugger-libs,mono/debugger-libs,Unity-Technologies/debugger-libs,Unity-Technologies/debugger-libs