OmegaConf.to_yaml does not handle Structured Configs

[omry]

1. DictConfigs annotated as Structured Configs triggers a type error from mypy:

@dataclass
class User:
    name: str = MISSING
    age: int = MISSING

cfg : User = OmegaConf.structured(User(name="Bond", age=7))
OmegaConf.to_yaml(cfg) # type error here

2. Other configish objects results in a runtime error:

OmegaConf.to_yaml(User)
OmegaConf.to_yaml(User(name="Bond", age=7))
OmegaConf.to_yaml({"name": "Bond", "age": 7})