Make a way to suppress MA0003

[jonathanpeppers]

I add a test to allow:

new UITextField().EditingDidBegin += _proxy.OnEditingDidBegin;

// This should warn, because it is NSObject
class UITextFieldProxy : NSObject
{
    // But then we suppressed the warning
    [UnconditionalSuppressMessage("Memory", "MA0003")]
    public void OnEditingDidBegin(object sender, EventArgs e) { }
}

I added code to look up the attribute on the method from this statement:

new UITextField().EditingDidBegin += _proxy.OnEditingDidBegin;

This also uncovered a bug in the analyzer:

--if (attribute.AttributeClass.ContainingNamespace.Name != "System.Diagnostics.CodeAnalysis")
++if (attribute.AttributeClass.ContainingNamespace.ToString() != "System.Diagnostics.CodeAnalysis")

In this example Name was just "CodeAnalysis". I have no idea why, but using .ToString() instead was successful. All tests pass with this change, so I'm going with it.