Provide strong reference version of API for PyWeakref_GetObject

[corona10]

PEP-703 explains the risky situation of borrowed reference API.
For working on #111926, I think that we should introduce a new API with strong reference that was named PyWeakref_FetchObject from the PEP.
But to follow the recent convention, the API name will be PyWeakref_GetObjectRef.

Since SC approved the PEP, there would be no issue with adding this API.
However I want to listen to opinions from a few core devs before working on the task.

@encukou @colesbury @vstinner

[colesbury]

I think @vstinner already added PyWeakref_GetRef that returns a strong reference.

[corona10]

I think @vstinner already added PyWeakref_GetRef that returns a strong reference.

Oh I see, then we close the issue.

[vstinner]

I think @vstinner already added PyWeakref_GetRef that returns a strong reference.

I'm living in the future! By the way, the beginning of my article https://vstinner.github.io/c-api-dict-getitemref.html tells about this API :-)