`typing.get_type_hints()` raises NameError when the target object
contains unresolavable type annotation (ex. TYPE_CHECKING).  This
handles the exception and use unresolved annotations for type hints.

An annotated instance variable on super class is not documented when
derived class has also other annotated instance variables because
`obj.__annotations__` is overrided by derived class's type hints.

To get annotations of the target class correctly, this scans MRO to
get all of annotated instance variables.

To control trimming doctest flags manually, this adds new options
:trim-doctest-flags: and :no-trim-doctest-flags: to doctest
directives.  It helps to describes doctest module itself in python
doc (see #6698).

Using "enum" for module name bothers me on debugging errors because
it sometimes raises ImportError.

This tries to import the parent object for the instance attribute
to get type annotations for the variable.

This allows the autosummary directive to take instance attributes to
build documents for them.

Add autosummary_filename_map config to avoid clashes