Support `enum.member` for python3.11+ (#17382)
There are no tests for `@enum.member` used as a decorator, because I can
only decorate classes and functions, which are not supported right now:
https://mypy-play.net/?mypy=latest&python=3.12&gist=449ee8c12eba9f807cfc7832f1ea2c49
```python
import enum
class A(enum.Enum):
class x: ...
reveal_type(A.x) # Revealed type is "def () -> __main__.A.x"
```
This issue is separate and rather complex, so I would prefer to solve it
independently.
Refs https://github.com/python/mypy/pull/17376
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Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
