Overload help - support for this/base overloads

[kindermannhubert]

Feature Description

E.g.:

class A { protected A(string s) { } }
class B : A { B() : base(/*here we want overload help*/) { } }

It's already pre-prepared with TODO in RoslynServices.GetOverloadsAsync.GetMemberGroup. There are some minor complications around getting the correct set of overloads.