The `SyntaxGenerator` adds `sealed` keyword for delegate types.

Example:
```C#
namespace Foo
{
    public delegate bool SyntaxReceiverCreator(int a, bool b);
}
```

After roundtrip: source -> ISymbol-> SyntaxGenerator -> source:

```C#
namespace Foo
{
    public sealed delegate bool SyntaxReceiverCreator(int a, bool b);
}
```

as a result: `Build falure: error CS0106: The modifier 'sealed' is not valid for this item `