python domain: Allow short type-names in info field lists

[tk0miya]

Is your feature request related to a problem? Please describe.
The info field lists can describe types of parameters, variables and a return value. But it requires full qualified name of the type.

.. py:function:: foo(x, y, z)

   :param sphinx.environment.BuildEnvironment x: OK
   :param BuildEnvironment y: NG; not a qualname

Full qualified name is unique and strict. But it is boring for marking up and hard to read.

Describe the solution you'd like

• Recognize the scope of the code?
• Give a special mark up like ~ (ex. :py:class:`~BuildEnvironment` )
• Special configuration like PYTHON_PATH?
• By some special configuration?

Describe alternatives you've considered
Nothing

Additional context

• refs: Could not link to Python's standard library #6100

[jakobandersen]

As a perhaps helpful pointer, the C++ domain does the scope tracking using env.ref_context to make sure the relevant data is present when cross-references are resolved.
Specifically for fields the process_field_xref method of the domain is used to update tracking (https://github.com/sphinx-doc/sphinx/blob/master/sphinx/domains/cpp.py#L7032).