Make nullable warnings a per file opt-in (#1842)

* Make nullable warnings a per file opt-in

* Remove unneeded compiler directives

* Remove compiler directive for User Data

src/Microsoft.SqlTools.ServiceLayer/SchemaCompare/SchemaCompareIncludeExcludeNodeOperation.cs

@@ -2,6 +2,8 @@
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 //
+
+#nullable disable
 using Microsoft.SqlServer.Dac.Compare;
 using Microsoft.SqlTools.ServiceLayer.SchemaCompare.Contracts;
 using Microsoft.SqlTools.ServiceLayer.TaskServices;