Add support for `dotnet test`

[jpobst]

With https://github.com/dotnet/android/pull/9470, we are now able to support dotnet run in .NET for Android projects. The next logical step would be to support dotnet test.

Ideally, this would probably take the form of a new ".NET for Android Test Project" template. Using this template, a user could write a test such as:

[Test]
public void Round () {
  Assert.AreEqual (3, Java.Lang.Math.Round (3.4));
}

Running dotnet test would:

• Compile the test project (including generating any needed test infrastructure)
• Deploy the test project
• Run the test project
• Transfer test results from device
• Display test results to user
• Output test results to output directory

Note from Discord:

Alexander Köplinger: this should be much easier with the new/upcoming mstest runner infra where the test is not a special project anymore but just a regular "executable"

We could definitely use dotnet test support like this in this repository instead of the custom infrastructure we currently have to run tests on emulators/devices.