Disable hash collision resistance for user data

MessagePack is not able to deserialize SuccessfulConflictResolution with
a collision resistant equality comparer due to the use of DocumentId as
a dictionary key.

src/Workspaces/Remote/Core/ServiceDescriptor.cs

@@ -58,7 +58,7 @@ protected override IJsonRpcMessageFormatter CreateFormatter()
             => ConfigureFormatter((MessagePackFormatter)base.CreateFormatter());
 
         private static readonly MessagePackSerializerOptions s_options = StandardResolverAllowPrivate.Options
-            .WithSecurity(MessagePackSecurity.UntrustedData)
+            .WithSecurity(MessagePackSecurity.UntrustedData.WithHashCollisionResistant(false))
             .WithResolver(CompositeResolver.Create(
                 MessagePackFormatters.GetFormatters(),
                 new IFormatterResolver[] { ImmutableCollectionMessagePackResolver.Instance, StandardResolverAllowPrivate.Instance }));