Akma/login migrations (#1728)

In this PR, we make the appropriate backend service changes in order to enable the login migrations feature in the SQL migration extension.

Changes include:

updating the Microsoft.SqlServer.Migration.Login NuGet version to the latest version
adding a new request handler for StartLoginMigrations calls, which makes the appropriate calls to the login NuGet
adding ExtensionMethod helper to properly combine exception maps login migration nuget calls

Co-authored-by: Akshay Mata <akma@microsoft.com>

src/Microsoft.SqlTools.ServiceLayer/Migration/Contracts/StartLoginMigration.cs

@@ -0,0 +1,135 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Microsoft.SqlServer.DataCollection.Common.Contracts.OperationsInfrastructure;
+using Microsoft.SqlTools.Hosting.Protocol.Contracts;
+using System.Collections.Generic;
+
+namespace Microsoft.SqlTools.ServiceLayer.Migration.Contracts
+{
+    /// <summary>
+    /// Represents the steps in login migration.
+    /// </summary>
+    public enum LoginMigrationStep
+    {
+        /// <summary>
+        /// Run pre-migration validations 
+        /// </summary>
+        StartValidations,
+
+        /// <summary>
+        /// Step to hash passwords and migrate logins
+        /// </summary>
+        MigrateLogins,
+
+        /// <summary>
+        /// Step to establish users and logins from source to target
+        /// </summary>
+        EstablishUserMapping,
+
+
+        /// <summary>
+        /// Step to migrate server roles
+        /// </summary>
+        MigrateServerRoles,
+
+        /// <summary>
+        /// Step to establish roles
+        /// </summary>
+        EstablishServerRoleMapping,
+
+        /// <summary>
+        /// Step to map all the grant/deny permissions for logins
+        /// </summary>
+        SetLoginPermissions,
+
+        /// <summary>
+        /// Step to map all server roles grant/deny permissions
+        /// </summary>
+        SetServerRolePermissions
+    }
+
+    public class StartLoginMigrationParams
+    {
+        /// <summary>
+        /// Connection string to connect to source 
+        /// </summary>
+        public string SourceConnectionString { get; set; }
+
+        /// <summary>
+        /// Connection string to connect to target
+        /// </summary>
+        public string TargetConnectionString { get; set; }
+
+        /// <summary>
+        /// List of logins to migrate
+        /// </summary>
+        public List<string> LoginList { get; set; }
+
+        /// <summary>
+        /// Azure active directory domain name (required for Windows Auth)
+        /// </summary>
+        public string AADDomainName{ get; set; }
+    }
+
+    public class LoginMigrationResult
+    {
+        /// <summary>
+        /// Start time of the assessment
+        /// </summary>
+        public IDictionary<string, IEnumerable<ReportableException>> ExceptionMap { get; set; }
+
+        /// <summary>
+        /// The login migration step that just completed
+        /// </summary>
+        public LoginMigrationStep CompletedStep { get; set; }
+
+        /// <summary>
+        /// How long this step took
+        /// </summary>
+        public string ElapsedTime{ get; set; }
+    }
+
+    public class StartLoginMigrationRequest
+    {
+        public static readonly
+            RequestType<StartLoginMigrationParams, LoginMigrationResult> Type =
+                RequestType<StartLoginMigrationParams, LoginMigrationResult>.Create("migration/startloginmigration");
+    }
+
+    public class ValidateLoginMigrationRequest
+    {
+        public static readonly
+            RequestType<StartLoginMigrationParams, LoginMigrationResult> Type =
+                RequestType<StartLoginMigrationParams, LoginMigrationResult>.Create("migration/validateloginmigration");
+    }
+
+    public class MigrateLoginsRequest
+    {
+        public static readonly
+            RequestType<StartLoginMigrationParams, LoginMigrationResult> Type =
+                RequestType<StartLoginMigrationParams, LoginMigrationResult>.Create("migration/migratelogins");
+    }
+
+    public class EstablishUserMappingRequest
+    {
+        public static readonly
+            RequestType<StartLoginMigrationParams, LoginMigrationResult> Type =
+                RequestType<StartLoginMigrationParams, LoginMigrationResult>.Create("migration/establishusermapping");
+    }
+    public class MigrateServerRolesAndSetPermissionsRequest
+    {
+        public static readonly
+            RequestType<StartLoginMigrationParams, LoginMigrationResult> Type =
+                RequestType<StartLoginMigrationParams, LoginMigrationResult>.Create("migration/migrateserverrolesandsetpermissions");
+    }
+
+    public class LoginMigrationNotification
+    {
+        public static readonly
+            EventType<LoginMigrationResult> Type =
+            EventType<LoginMigrationResult>.Create("migration/loginmigrationnotification");
+    }
+}