[mypyc] property setter and deleter don't work with parameterized attributes

Bug Report

mypyc fails to compile a class with a property setter and deleter and a weakref attribute.

To Reproduce

1. Defined (in a file foo.py) a class Bar with a property that has a setter and deleter and weakref attribute.
2. run mypyc foo.py3.

e.g.

from __future__ import annotations
from typing import TypeVar, Generic
import weakref

T = TypeVar("T")

class Bar(Generic[T]):
    _attr: weakref.ReferenceType[T] | None
    def __init__(self) -> None:
        self._attr = None
    @property
    def attr(self) -> T | None:
        return self._attr() if self._attr is not None else None
    @attr.setter
    def attr(self, value: T) -> None:
        self._attr = weakref.ref(value)
    @attr.deleter
    def attr(self) -> None:
        self._attr = None

Actual Behavior

I get the following error:

File "mypyc/irbuild/classdef.py", line 87, in transform_class_def
File "mypyc/irbuild/classdef.py", line 200, in add_method
File "mypyc/irbuild/function.py", line 369, in handle_ext_method
File "mypyc/irbuild/function.py", line 312, in gen_func_item
File "mypyc/irbuild/function.py", line 351, in gen_func_ir
...: KeyError: <mypy.nodes.FuncDef object at 0x7f93d4876b80>

This error does not occur when setter and deleter are omitted.

Your Environment

• Mypy version used: 0.950
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.9
• Operating system and version: macOS Monterey, version 12.4

Reproduce the failure with the foo.py example, then trace the reported path through mypyc/irbuild/classdef.py and mypyc/irbuild/function.py. Add coverage for a parameterized attribute with property setter and deleter, and consider the issue done when mypyc foo.py compiles it without the KeyError.