__del__ method is not called

Steps to Reproduce

If we have a class with __del__ method:

import sys


class Foo:
    def __init__(self, name):
        self.name = name

    def __del__(self):
        sys.stdout.write(self.name + '\n')

Running the following statements with CPython,

def func():
    foo = Foo('Foo 1')
    bar = Foo('Foo 2')
    del bar

func()
foo = Foo('Foo 3')
foo = Foo('Foo 4')

[Expected behavior:]
will get output

Foo 2
Foo 1
Foo 3
Foo 4

[Actual behavior:]
But running with IronPython, there's nothing output.

This blocks #938. FileIO, TextIOWrapper etc classes have finalizer (defined in their base class _IOBase) calling close(). But the finalizer is never called.

Start by running the provided reproduction in CPython and IronPython, then trace how the __del__ method is handled for the sample Foo objects. Check the _IOBase finalizer path mentioned in the issue as well. Done means finalizers run with the expected output and classes such as FileIO and TextIOWrapper can close through their finalizers.