Error on subclassing Dict[Any, ...]

[Jasha10]

Based on #502 (comment), it is proposed to deprecate support for structured configs that subclass Dict[Any, ...], with only subclasses of Dict[str, ...] being supported going forward.

For example, creating a structured config node based on the following dataclass would issue a deprecation warning,

@dataclass
class MyConf(Dict[int, Any]):
    ...

while a structured config node based on the following would be fully supported:

@dataclass
class MyConf(Dict[str, Any]):
    ...

[omry]

class MyConf(Dict[int, Any])

This is not supported in 2.0, we can just straight to error with it.

[omry]

I think the idea is that this is is a reminder for 2.2 to remove the deprecation warning from extending Dict and make it an error. (We can also just allow but completely ignore it).

[Jasha10]

I thought the idea was that subclassing Dict[str, str] is deprecated and subclassing Dict[int, str] or Dict[Any, str] should throw an error...

If you still want to go that route, I can try to get a PR ready tonight.

[omry]

Oh yeah, sorry.

[Jasha10]

Closing since we've already deprecated subclassing Dict in general.