DebuggerTypeProxyAttribute does not work when compiled against .NETCore

The C# EE is not handling proxy type names correctly (for Windows Store or Silverlight apps) if the proxy type is a nested type within a generic class.
Fix is to move the proxy types outside of the generic collection class for each collection type. This fixes the issue against VS2013 and also works with VS2015.
Note that for VS2015, C# EE has itself been fixed to handle this case correctly