`_PyWeakref_ClearRef` and `_PyWeakref_ClearWeakRefsExceptCallbacks` should be exposed in 3.13

[colesbury]

_PyWeakref_ClearRef was previously exposed in the public C-API. In 3.13, it was moved to pycore_weakref.h and the symbol is not exposed (i.e., it's extern void instead of PyAPI_FUNC(void).

_PyWeakref_ClearRef is used to clear a single weakref without calling its callback. _PyWeakref_ClearWeakRefsExceptCallbacks is the thread-safe version. If people are using _PyWeakref_ClearRef, we'd rather they use _PyWeakref_ClearWeakRefsExceptCallbacks so that the code is thread-safe in the free-threading build.

One use case is to clear newly added weakrefs after you've called a finalizer, in case your C type does not delegate to subtype_dealloc.

Uses:

• PyTorch
• shiboken2 (might be old)
• Nuitka

At a minimum, we should add PyAPI_FUNC to _PyWeakref_ClearRef and _PyWeakref_ClearWeakRefsExceptCallbacks and consider making _PyWeakref_ClearWeakRefsExceptCallbacks part of the public C API.

Linked PRs

• gh-118789: Restore hidden _PyWeakref_ClearRef #118797
• gh-118789: Add PyUnstable_Object_ClearWeakRefsNoCallbacks #118807
• [3.13] gh-118789: Restore hidden _PyWeakref_ClearRef (GH-118797) #118903
• [3.13] gh-118789: Add PyUnstable_Object_ClearWeakRefsNoCallbacks (GH-118807) #120695