Per editor Connect support v0.1

- Basic plumbing to support connections for a URI rather than global connections. Typical use case is editor requests to connect, but this isn't the only possible use
- Tests pass but need updating to cover new functionality, and re-enable AutoCompleteService test once there is a ServiceDiscovery component that registers and returns services. This is necessary as .Instance won't allow for dependency injection and proper testing.

src/Microsoft.SqlTools.ServiceLayer/Hosting/Protocol/IMessageSender.cs

@@ -8,7 +8,7 @@ using Microsoft.SqlTools.ServiceLayer.Hosting.Protocol.Contracts;
 
 namespace Microsoft.SqlTools.ServiceLayer.Hosting.Protocol
 {
-    internal interface IMessageSender
+    public interface IMessageSender
     {
         Task SendEvent<TParams>(
             EventType<TParams> eventType,

src/Microsoft.SqlTools.ServiceLayer/Hosting/Protocol/IProtocolEndpoint.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.SqlTools.ServiceLayer.Hosting.Protocol.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.Hosting.Protocol
+{
+    /// <summary>
+    /// A ProtocolEndpoint is used for inter-process communication. Services can register to
+    /// respond to requests and events, send their own requests, and listen for notifications
+    /// sent by the other side of the endpoint
+    /// </summary>
+    public interface IProtocolEndpoint : IMessageSender
+    {
+        void SetRequestHandler<TParams, TResult>(
+            RequestType<TParams, TResult> requestType,
+            Func<TParams, RequestContext<TResult>, Task> requestHandler);
+
+        void SetEventHandler<TParams>(
+            EventType<TParams> eventType,
+            Func<TParams, EventContext, Task> eventHandler);
+
+        void SetEventHandler<TParams>(
+            EventType<TParams> eventType,
+            Func<TParams, EventContext, Task> eventHandler,
+            bool overrideExisting);
+    }
+}

src/Microsoft.SqlTools.ServiceLayer/Hosting/Protocol/ProtocolEndpoint.cs

@@ -16,7 +16,7 @@ namespace Microsoft.SqlTools.ServiceLayer.Hosting.Protocol
     /// Provides behavior for a client or server endpoint that
     /// communicates using the specified protocol.
     /// </summary>
-    public class ProtocolEndpoint : IMessageSender
+    public class ProtocolEndpoint : IMessageSender, IProtocolEndpoint
     {
         private bool isStarted;
         private int currentMessageId;