Add stubs for ldap3

[srittau]

Best reviewed commit by commit. First commit is stubgen + black + isort - imports.

[Akuli]

(env) akuli@akuli-desktop:~/typeshed/env/lib/python3.9/site-packages/ldap3$ grep -r 'except ImportError'
utils/tls_backport.py:except ImportError:
utils/log.py:except ImportError:  # NullHandler not present in Python < 2.7
utils/ciDict.py:except ImportError:
utils/uri.py:except ImportError:
utils/ntlm.py:                except ImportError:
protocol/sasl/kerberos.py:except ImportError:
protocol/sasl/kerberos.py:    except ImportError:
protocol/sasl/kerberos.py:    except ImportError:
protocol/formatters/formatters.py:except ImportError:
extend/standard/PersistentSearch.py:except ImportError:  # Python 2
extend/microsoft/persistentSearch.py:except ImportError:  # Python 2
core/tls.py:except ImportError:
core/tls.py:except ImportError:
core/tls.py:except ImportError:
core/server.py:except ImportError:
core/server.py:except ImportError:
strategy/asyncStream.py:except ImportError:  # Python 2
strategy/reusable.py:except ImportError:  # Python 2
strategy/base.py:except ImportError:
abstract/entry.py:except ImportError:
__init__.py:    except ImportError:

Maybe we should check if the # Python 2 lines (maybe others too) need manual cleanup.

[srittau]

I'm sure there is quite a lot of Python 2 cleanup possible.

[Akuli]

Note to self: reviewed the beginning of 8effa8e and everything before it

[Akuli]

Finished reviewing 8effa8e

[Akuli]

Reviewing done

[Akuli]

Didn't read the first commit.