autodoc typehints fail to resolve types when a function parameter is assigned a default value that is an enum value.

Describe the bug
When using automodule, if a function parameter is an enum and is assigned a default value, all parameters appear to fail to process.

To Reproduce

Simple doc file index.rst:

Hello World
===========

code docs
=========

.. automodule:: helloworld.helloworld
    :members:
    :undoc-members:
    :show-inheritance:

Here's an example module helloworld.py:

from enum import Enum

class MyEnum(Enum):
    FIRST = 1
    SECOND = 2
    THIRD = 3

class OtherClass():
    pass

class Example1:
    """Parameter types link correctly here"""
    def __init__(self,
                 param1: OtherClass,
                 param2: MyEnum):
        pass

    def foo(self,
            param1: OtherClass,
            param2: MyEnum):
        pass

class Example2:
    """When an enum is assigned a default value no type links are resolved"""
    def __init__(self,
                 param1: OtherClass,
                 param2: MyEnum = MyEnum.FIRST):
        pass

    def foo(self,
            param1: OtherClass,
            param2: MyEnum = MyEnum.FIRST):
        pass

class Example3:
    """When an enum is assigned a default value no type links are resolved"""
    def __init__(self,
                 param1: OtherClass,
                 param2: MyEnum = MyEnum(1)):
        pass

Expected behavior
I expect the enum types to resolve correctly and link to the enum definition.
I expect the other parameters to also resolve their types and link their definitions as well.
A nice-to-have would be for the enum value link to the value in the enum definition as well.

Your project
I've included a simple example above

Screenshots
Here's the generated documentation. See how Example1 resolves the types correctly but Example2 does not.

Environment info

• OS: Ubuntu 18.04, Ubuntu 20.04
• Python version: 3.6.9, 3.8.2
• Sphinx version: 3.1.2, 3.2.1
• Sphinx extensions: sphinx.ext.autodoc
• Extra tools: Viewing output on Chrome

Additional context

Reproduce the issue with the supplied index.rst and helloworld.py examples, comparing Example1 with Example2 and Example3. Trace Sphinx autodoc's type-hint resolution from the automodule entry point; done means enum parameter types and the other parameter types link to their definitions when defaults are present.