Record synthesized implementation of PrintMembers calls object overload for string

See https://godbolt.org/z/c7cGhGoK1. I can't tell if this is a spec bug or a product bug. The spec seems to imply that the record implementation of PrintMembers should call

```C#
protected virtual bool PrintMembers(StringBuilder builder)
{
builder.Append(nameof(P1));
builder.Append(" = ");
builder.Append(this.P1);

return true;
}
```

In the case that `P1` is a string, overload resolution would pick the `string` overload. Instead it calls the object overload.