Infer the type of Enumerable.Empty and similar constructs based on return types

[ekolis]

If I have a method like so:

public IEnumerable<int> GetEmptyNumberList()
{
    return Enumerable.Empty();
}

I get a compile error saying that the type parameter of Enumerable.Empty() cannot be inferred. It would be nice if this were possible so we don't have to go duplicating the return type.

[PathogenDavid]

This has been requested before: #92