gh-91544: Better stringification of Parameter defaults

[ucodery]

Examples from the issue, redone under this commit:

>>> import inspect
>>> def a_test(a=str, b=inspect, c=inspect.Signature, d=inspect.signature, e=inspect.Signature.replace, f=(i for i in range(3))):
...    """lots of objects with awkward reprs"""
...
>>> print(inspect.signature(a_test))
(a=str, b=inspect, c=inspect.Signature, d=inspect.signature, e=inspect.Signature.replace, f=<genexpr>)
>>>
>>> def b_test(a: str = str):
...    """annotations seem to get this right"""
...
>>> print(inspect.signature(b_test))
(a: str = str)

>>> help(locale.atof)
Help on function atof in module locale:

atof(string, func=float)
    Parses a string as a float according to the locale settings.

#91544