Don't perform dynamic registration of server capabilities if client does not support any kind of dynamic registration.

As noted by LSP protocol docs, clients do not have to support this:

https://github.com/Microsoft/language-server-protocol/blob/master/protocol.md#new-register-capability

Author: tintoy

src/Lsp/LanguageServer.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.IO;
@@ -213,6 +213,9 @@ private async Task DynamicallyRegisterHandlers()
                 registrations.Add(handler.Registration);
             }
 
+            if (registrations.Count == 0)
+                return; // No dynamic registrations supported by client.
+
             var @params = new RegistrationParams() { Registrations = registrations };
 
             await this.RegisterCapability(@params);
@@ -260,4 +263,4 @@ public void Dispose()
 
         public IDictionary<string, JToken> Experimental { get; } = new Dictionary<string, JToken>();
     }
-}
+}