Support for Python 3.12 type aliases in structured configs

[tmke8]

Is your feature request related to a problem? Please describe.

I would like to be able to define type aliases and use them in structured configs:

from pathlib import Path

# new type alias syntax
type StrOrPath = str | Path

@dataclass
class C:
    path: StrOrPath

However, this currently doesn't work:

Full example with traceback.

>>> from dataclasses import dataclass
>>> type Int = int
>>> @dataclass
... class C:
...   x: Int
... 
>>> from omegaconf import OmegaConf
>>> conf1 = OmegaConf.structured(C)          
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/omegaconf.py", line 125, in structured
    return OmegaConf.create(obj, parent, flags)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/omegaconf.py", line 178, in create
    return OmegaConf._create_impl(
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/omegaconf.py", line 900, in _create_impl
    format_and_raise(node=None, key=None, value=None, msg=str(e), cause=e)
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 819, in format_and_raise
    _raise(ex, cause)
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 797, in _raise
    raise ex.with_traceback(sys.exc_info()[2])  # set env var OC_CAUSE=1 for full trace
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/omegaconf.py", line 861, in _create_impl
    return DictConfig(
           ^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/dictconfig.py", line 111, in __init__
    format_and_raise(node=None, key=key, value=None, cause=ex, msg=str(ex))
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 819, in format_and_raise
    _raise(ex, cause)
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 797, in _raise
    raise ex.with_traceback(sys.exc_info()[2])  # set env var OC_CAUSE=1 for full trace
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/dictconfig.py", line 94, in __init__
    self._set_value(content, flags=flags)
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/dictconfig.py", line 647, in _set_value
    raise e
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/dictconfig.py", line 644, in _set_value
    self._set_value_impl(value, flags)
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/dictconfig.py", line 674, in _set_value_impl
    data = get_structured_config_data(value, allow_objects=ao)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 495, in get_structured_config_data
    return get_dataclass_data(obj, allow_objects=allow_objects)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 421, in get_dataclass_data
    format_and_raise(
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 899, in format_and_raise
    _raise(ex, cause)
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 797, in _raise
    raise ex.with_traceback(sys.exc_info()[2])  # set env var OC_CAUSE=1 for full trace
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/_utils.py", line 413, in get_dataclass_data
    d[name] = _maybe_wrap(
              ^^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/omegaconf.py", line 1105, in _maybe_wrap
    return _node_wrap(
           ^^^^^^^^^^^
  File "/home/tmk/dev/python/py12proj/.venv/lib/python3.12/site-packages/omegaconf/omegaconf.py", line 1087, in _node_wrap
    raise ValidationError(f"Unexpected type annotation: {type_str(ref_type)}")
omegaconf.errors.ValidationError: Unexpected type annotation: Int
    full_key: x
    object_type=C

Describe the solution you'd like

I think what needs to be done is, the code needs to check for the TypeAliasType objects that are produced by type T = ... and then unwrap the type.

Describe alternatives you've considered
Not using new type alias syntax.