C#: Additional tracking of lambdas through fields and properties

[hvitved]

This PR adds support for tracking lambdas through fields and (field-like) properties, but (currently) limited to assignments in constructors and uses in instance methods:

class C
{
    private Action a;

    public C(Action a)
    {
        this.a = a; // (1)
    }

    public void CallAction()
    {
        this.a(); // (2)
    }

    public void SetAction(Action a)
    {
        this.a = a; // (3)
    }
}

That is, we will track lambdas from (1) to (2), but not from (2) to (3). This restriction is because the data flow algorithm for tracking lambdas is not field-sensitive, hence we need to model field stores/reads as jump steps, and therefor apply the conservative restriction above.

I spot checked a few of the new results, and they are indeed the result of more lambda calls being resolvable.

[tamasvajk]

Looks plausible to me.