Cancel running requests when the connection terminates (#78525)

Thinking this might be the cause of some exceptions we are seeing in
shutdown.

Author: dibarbet

src/LanguageServer/Microsoft.CommonLanguageServerProtocol.Framework/AbstractLanguageServer.cs

@@ -65,6 +65,9 @@ protected AbstractLanguageServer(
         _jsonRpc = jsonRpc;
         TypeRefResolver = typeRefResolver ?? TypeRef.DefaultResolver.Instance;
 
+        // We have no need to continue running LSP requests after the connection is closed.
+        _jsonRpc.CancelLocallyInvokedMethodsWhenConnectionIsClosed = true;
+
         _jsonRpc.AddLocalRpcTarget(this);
         _jsonRpc.Disconnected += JsonRpc_Disconnected;
         _lspServices = new Lazy<ILspServices>(() => ConstructLspServices());