Create MS.SqlTools.Credentials project (#249)

* Initial credential service files

* Clean-up hostloader

* Update build scripts to build credentials archive

* Move hosting files to new assembly

* Add credentials files to MS.SqlTools.Credentials

* Remove duplicate files

* Update namespace in program.cs

* Fix test build breaks

* Update extensions visibility.

* Remove unused resource strings

* Add xproj files to SLN for appveyor builds

* Fix appveyor build break in test project

* Fix extensibility tests

* Fix various typos in latest iteration

* Add settings for Integration build

* Fix codecoverage.bat to use full pdb for new projects

* Fix bug when packing in folder with native images

* Fix typos in xproj

* Reset XLF to fix build.cmd

src/Microsoft.SqlTools.Hosting/Hosting/Protocol/Channel/ChannelBase.cs

@@ -0,0 +1,81 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Threading.Tasks;
+using Microsoft.SqlTools.ServiceLayer.Hosting.Protocol.Serializers;
+
+namespace Microsoft.SqlTools.ServiceLayer.Hosting.Protocol.Channel
+{
+    /// <summary>
+    /// Defines a base implementation for servers and their clients over a
+    /// single kind of communication channel.
+    /// </summary>
+    public abstract class ChannelBase
+    {
+        /// <summary>
+        /// Gets a boolean that is true if the channel is connected or false if not.
+        /// </summary>
+        public bool IsConnected { get; protected set; }
+
+        /// <summary>
+        /// Gets the MessageReader for reading messages from the channel.
+        /// </summary>
+        public MessageReader MessageReader { get; protected set; }
+
+        /// <summary>
+        /// Gets the MessageWriter for writing messages to the channel.
+        /// </summary>
+        public MessageWriter MessageWriter { get; protected set; }
+
+        /// <summary>
+        /// Starts the channel and initializes the MessageDispatcher.
+        /// </summary>
+        /// <param name="messageProtocolType">The type of message protocol used by the channel.</param>
+        public void Start(MessageProtocolType messageProtocolType)
+        {
+            IMessageSerializer messageSerializer = null;
+            if (messageProtocolType == MessageProtocolType.LanguageServer)
+            {
+                messageSerializer = new JsonRpcMessageSerializer();
+            }
+            else
+            {
+                messageSerializer = new V8MessageSerializer();
+            }
+
+            this.Initialize(messageSerializer);
+        }
+
+        /// <summary>
+        /// Returns a Task that allows the consumer of the ChannelBase
+        /// implementation to wait until a connection has been made to
+        /// the opposite endpoint whether it's a client or server.
+        /// </summary>
+        /// <returns>A Task to be awaited until a connection is made.</returns>
+        public abstract Task WaitForConnection();
+
+        /// <summary>
+        /// Stops the channel.
+        /// </summary>
+        public void Stop()
+        {
+            this.Shutdown();
+        }
+
+        /// <summary>
+        /// A method to be implemented by subclasses to handle the
+        /// actual initialization of the channel and the creation and
+        /// assignment of the MessageReader and MessageWriter properties.
+        /// </summary>
+        /// <param name="messageSerializer">The IMessageSerializer to use for message serialization.</param>
+        protected abstract void Initialize(IMessageSerializer messageSerializer);
+
+        /// <summary>
+        /// A method to be implemented by subclasses to handle shutdown
+        /// of the channel once Stop is called.
+        /// </summary>
+        protected abstract void Shutdown();
+    }
+}