[3.14] gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original...

[3.14] gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible (GH-136893) (#136960)

gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible (GH-136893)

An interesting hack, but more localized in scope than GH-135230.

This may be a breaking change if people intentionally keep the original class around
when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the
original class.
(cherry picked from commit 46cbdf967ada11b0286060488b61635fd6a2bb23)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>