* Remove lots of duplicated code
* Add support for testing external code elements

Fix #2356 Return Attributes  CodeElements for Get/Set Methods of
Properties in both C# and VB

Fixes Internal TFS issue 1147885

CodeModel service should get the name of the parameter from the
SyntaxNode rather than the symbols since we need to get the fullname
used in the source code.

Implement AddAttribute so that it works for Declare functions/subs,
auto-properties, simple and custom events, and MustOverfide
functions/subs. This fixes Issue #596.

VB CodeModel now returns proper EnvDTE80.vsCMFunction2 values for
AddHandler, RemoveHandler and RaiseEvent accessors.