Support nested class controls

[exyi]

Since controls got shorter and easier to write, it would make sense to allow nested class to be controls. At least in tests it would be quite useful.

class SomeTests {
    public class MyControl {
         ....
    }

    [TestMethod]
    public void Test() {

        await cth.RunPage(typeof(BasicTestViewModel), @"
                <cc:MyControl TagName=div />
                "
            );
      }
}

It's currently not possible to use the control in dothtml markup