Support functional API for Enum *Subclasses* too

Tested with version 0.641.

The functional API for enums is only supported on Enum itself, and not subclasses (that do not override the relevant methods). I hit this using the OrderedEnum suggestion from the standard library documentation: https://docs.python.org/3/library/enum.html#orderedenum.

Running on:

from enum import Enum

class Foo(Enum):
    ""

Bar: type = Enum('Bar', ['X', 'Y']) # line 6
Baz: type = Foo('Baz', ['X', 'Y']) # line 7

bar: Bar = Bar.X # line 9
baz: Baz = Baz.Y # line 10

gives

asdf.py:7: error: Incompatible types in assignment (expression has type "Foo", variable has type "type")
asdf.py:7: error: Too many arguments for "Foo"
asdf.py:10: error: Invalid type "asdf.Baz"
asdf.py:10: error: "type" has no attribute "Y"

Note that 6 is deemed fine, but 7 causes complaints. I'd hope for both lines to be fine.

The even larger issue is that annotations using Baz totally fail too: Line 9 is deemed fine but 10 fails. I wouldn't mind the obscure use of the Enum subclass failing if it weren't for the fact that every annotation with my nice enum type won't work.

issue の reproducer から始め、Enum サブクラスに対する Enum の functional API を mypy がどのように処理しているかを追跡してください。Foo('Baz', ['X', 'Y']) の推論される型と、Baz を使用するアノテーションがどのように処理されるかを確認してください。サブクラスの factory 呼び出しと Baz 型のメンバーの両方が、報告されているエラーなしに型チェックを通れば完了です。