Multiple GQLUda instances are ignored

I know the normal usage is to do:

```d
@GQLDUda(uda1, uda2) int member;
```

But if you happen to do:

```d
@GQLDUda(uda1) @GQLDUda(uda2) int member;
```

The first is the only one obeyed. The code should use both, or provide an error saying that only one is allowed. The former solution is preferred, so you can split out common attributes into a scope.