Commented Task: Query: Consider switching to public LINQ expression visitor [10]

Currently EF has its own copy of the LINQ expression visitor that started as a copy of the internal expression visitor. Since then, in .NET 4.0 the expression visitor was made public, so in theory we could be using it now. If there are differences (we have fixed bugs, they have fixed bugs as well) we can consider extending. This is part of the effort to simplify our code base by getting rid of our own custom classes that are redundants with other types in the frameowrk (e.g. singleton, memoizer, and any custom collections we could be using).
Comments: **EF Team Triage:** We'll tackle this after EF6 because this is purely a code improvement task and the current code behaves correctly.