Fixes sphinx-doc/sphinx#8114

https://github.com/sphinx-doc/sphinx/pull/8037#issuecomment-673511490

`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.

So far, napoleon converts multiple paramaters declrarations to single
paramaeter fields (`:param:` and `:type:`) unexpectedly.  As a result,
the output seems broken.

This converts it to multiple parameter fields (a pair of field for each
parameter declration) to build parameter successfully.

Note: The conversion rule is available only when napoleon_use_params=True.

Fix a testcase that added just before #8049 merged.

enable type preprocessing without use_param