brain_attrs doesn't add PEP 526 instance variable annotations, causing `no-member` errors

[Hnasar]

Steps to reproduce

In some contexts, Pylint issues a false positive with an attrs class with only a type annotation (see PEP 526. If we add the attribute via the astroid brain_attrs then this fixes the issue. (I'm not sure if this is a duplicate of #724 ). This is supported at runtime with the newer attrs decorators.

# pylint: disable=missing-docstring,too-few-public-methods,unnecessary-lambda-assignment
import attrs  # pylint: disable=import-error

@attrs.define
class AttrsCls:
    x: int

ac = AttrsCls(1)
ac.x += 1

Current behavior

regression_xxxx_attrs_no_member.py:13: [E1101(no-member), ] Instance of 'AttrsCls' has no 'x' member

Expected behavior

No error

[jacobtylerwalls]

Marking as blocker to ensure we forwardport the fix before the next feature release.

[jacobtylerwalls]

I guess we'll just take care of the forwardport when merging maintenance into main.