gh-106320: Move private _PyGen API to the internal C API

[vstinner]

Move private _PyGen API to internal C API:

• _PyAsyncGenAThrow_Type
• _PyAsyncGenWrappedValue_Type
• _PyCoroWrapper_Type
• _PyGen_FetchStopIterationValue()
• _PyGen_Finalize()
• _PyGen_SetStopIterationValue()

No longer these symbols, except of the ones by the _asyncio shared extensions.

• Issue: C API: Remove private C API functions (move them to the internal C API) #106320

[rdb]

If _PyGen_FetchStopIterationValue is no longer public, what is the supported replacement we should use in our project?

[vstinner]

@rdb:

If _PyGen_FetchStopIterationValue is no longer public, what is the supported replacement we should use in our project?

Would you mind to open a new issue to request a public replacement function? Please explain how you use this function, and how existing API is not enough.

[rdb]

@vstinner We've switched to using PyErr_GetRaisedException() and extracting the value from there (see this commit), so as long as the structure of PyStopIterationObject remains part of the public ABI, I think we're good.

[vstinner]

When can add a public function. Just open an issue to ask for it, so we can discuss the issue and decide if it's worth it

[rdb]

It's not necessary, unless you're telling me that PyStopIterationObject is going to become opaque in the future.