Allow async test methods for UITestMethod on UWP and WinUI

[Youssef1313]

Fixes #5306

[marcelwgn]

Uhm, how does this address #740? The former is about being able to use datarows with UITests, this PR on the other hand allows using async on tests right?

[Youssef1313]

@marcelwgn The original issue description is inaccurate. Based on the comments/discussions there, the real issue is really just UITestMethodAttribute deadlocking. Using parameterized tests does not require DataTestMethodAttribute, and so we should not introduce UIDataTestMethodAttribute as it doesn't serve any purpose.

[marcelwgn]

So the following test should work then?

[UITestMethod]
[DataRow(0)]
[DataRow(1)]
[DataRow(2)]
public void TestMethod2(int index)
{
    var grid = new Grid
    {
        MinWidth = index
    };

    grid.UpdateLayout();

    Assert.AreEqual(index, grid.ActualWidth);
}

Because when I run it in Visual Studio, I get the following issue:

    Cannot run test method 'App8.UnitTest1.TestMethod2': Test data doesn't match method parameters. Either the count or types are different.
Test expected 1 parameter(s), with types 'Int32',
but received 0 argument(s), with types ''.

The thread in that issue evolved to providing a workaround to that missing capability using async tests that would essentially implement the behaviour that UITestMethod should support, but that requires async which is not supported. I disagree that the original issue description is misleading, the above sample does not work so there still is no support for this. ALlowing async would just allow for a workaround to work.

[Youssef1313]

It's supposed to work. I'll check why it doesn't work, but that wasn't what I understood from the follow-up comments.

[Youssef1313]

@marcelwgn This should be working if you are using the latest MSTest. I could repro only with really old versions of MSTest that are not supported.