OmegaConf.structured raises exception on tuple

[jieru-hu]

This seems to be a regression. Although we do not officially support tuple, we should probably still keep supporting this for backward compatibility.

to repro

from dataclasses import dataclass
from typing import Optional
from omegaconf import OmegaConf

@dataclass
class Config:
    vision_layers: Optional[tuple] = (3, 6, 4, 3)

print(OmegaConf.structured(Config))

on OC 2.1.1

 % python repro.py
{'vision_layers': [3, 6, 4, 3]}

on OC 2.2.2

% python repro.py
Traceback (most recent call last):
  File "/Users/jieru/workspace/hydra/repro/repro.py", line 9, in <module>
    print(OmegaConf.structured(Config))
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/omegaconf.py", line 123, in structured
    return OmegaConf.create(obj, parent, flags)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/omegaconf.py", line 176, in create
    return OmegaConf._create_impl(
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/omegaconf.py", line 882, in _create_impl
    format_and_raise(node=None, key=None, value=None, msg=str(e), cause=e)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 793, in format_and_raise
    _raise(ex, cause)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 771, in _raise
    raise ex.with_traceback(sys.exc_info()[2])  # set env var OC_CAUSE=1 for full trace
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/omegaconf.py", line 843, in _create_impl
    return DictConfig(
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/dictconfig.py", line 111, in __init__
    format_and_raise(node=None, key=key, value=None, cause=ex, msg=str(ex))
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 793, in format_and_raise
    _raise(ex, cause)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 771, in _raise
    raise ex.with_traceback(sys.exc_info()[2])  # set env var OC_CAUSE=1 for full trace
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/dictconfig.py", line 94, in __init__
    self._set_value(content, flags=flags)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/dictconfig.py", line 649, in _set_value
    raise e
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/dictconfig.py", line 646, in _set_value
    self._set_value_impl(value, flags)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/dictconfig.py", line 676, in _set_value_impl
    data = get_structured_config_data(value, allow_objects=ao)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 481, in get_structured_config_data
    return get_dataclass_data(obj, allow_objects=allow_objects)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 409, in get_dataclass_data
    format_and_raise(
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 873, in format_and_raise
    _raise(ex, cause)
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 771, in _raise
    raise ex.with_traceback(sys.exc_info()[2])  # set env var OC_CAUSE=1 for full trace
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/_utils.py", line 401, in get_dataclass_data
    d[name] = _maybe_wrap(
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/omegaconf.py", line 1070, in _maybe_wrap
    return _node_wrap(
  File "/Users/jieru/miniconda3/envs/hydra39/lib/python3.9/site-packages/omegaconf/omegaconf.py", line 1052, in _node_wrap
    raise ValidationError(f"Unexpected object type: {type_str(ref_type)}")
omegaconf.errors.ValidationError: Unexpected object type: tuple
    full_key: vision_layers
    object_type=Config

[jieru-hu]

cc @pixelb @Jasha10 this is blocking internal upgrade