In debug builds, if a debugger is attached, don't cancel async calls

By switching to None cancellation token, we make it easier to debug and
pause for longer times while inspecting the code generation from within
the IDE, that would otherwise be canceled automatically by VS.

src/Proxy/Proxy.Generator/ProxyGenerator.cs

@@ -246,7 +246,7 @@ public static (string name, SyntaxNode syntax) CreateProxy(ImmutableArray<ITypeS
                                 modifiers: DeclarationModifiers.Partial,
                                 baseType: baseType == null ? null : generator.IdentifierName(baseType.Name),
                                 interfaceTypes: interfaceTypes.Select(x => generator.IdentifierName(x.Name))),
-                            generator.Attribute(nameof(CompilerGeneratedAttribute))
+                            generator.Attribute("CompilerGenerated")
                         )
                     )
                 }));
@@ -256,6 +256,11 @@ public static (string name, SyntaxNode syntax) CreateProxy(ImmutableArray<ITypeS
 
         public static async Task<Document> ApplyVisitors(Document document, ICodeAnalysisServices services, CancellationToken cancellationToken)
         {
+#if DEBUG
+            if (Debugger.IsAttached)
+                cancellationToken = CancellationToken.None;
+#endif
+
             var language = document.Project.Language;
             var prepares = services.GetLanguageServices<IDocumentVisitor>(language, DocumentVisitorLayer.Prepare).ToArray();
             foreach (var prepare in prepares)