Migrate test projects from xunit 2.9.3 to xunit.v3 3.2.2

Test projects become executables (OutputType=Exe) as required by v3.
Satisfy the new xUnit1051 analyzer by passing TestContext cancellation
tokens in the generator compilation test.

tests/MrGameEng.Assets.Generator.Tests/AssetHandlesGeneratorTests.cs

@@ -109,13 +109,15 @@ public class AssetHandlesGeneratorTests
 
         var compilation = CSharpCompilation.Create(
             "generated",
-            [CSharpSyntaxTree.ParseText(source), CSharpSyntaxTree.ParseText(stubs)],
+            [CSharpSyntaxTree.ParseText(source, cancellationToken: TestContext.Current.CancellationToken),
+             CSharpSyntaxTree.ParseText(stubs, cancellationToken: TestContext.Current.CancellationToken)],
             [MetadataReference.CreateFromFile(typeof(object).Assembly.Location),
              MetadataReference.CreateFromFile(System.Runtime.Loader.AssemblyLoadContext.Default
                  .LoadFromAssemblyName(new System.Reflection.AssemblyName("System.Runtime")).Location)],
             new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
 
-        var errors = compilation.GetDiagnostics().Where(d => d.Severity == DiagnosticSeverity.Error).ToList();
+        var errors = compilation.GetDiagnostics(TestContext.Current.CancellationToken)
+            .Where(d => d.Severity == DiagnosticSeverity.Error).ToList();
         Assert.Empty(errors);
     }