Close #6830: autodoc: consider a member private if docstring contains :private:

[tk0miya]

Feature or Bugfix

• Feature

Purpose

• refs: A ".. private:: True/False" directive to override whether autodoc/autosummary treat a member as private (regardless of underscores) #6830

• autodoc considers a member private if its docstring contains :private: field in its info-field-list

  For example:

  def func(name):
    """blah blah blah
  
    :param name: description of name
    :type name: str
    :private:
    """
  

[tk0miya]

Side note: I thought adding :private: on the top of docstring at first. But I noticed it conflicts with autodoc_docstring_signature feature. So I chose info-field-list to specify its attribute finally.

[shimizukawa]

LGTM!

[tk0miya]

Thank you for reviewing. merged!