gh-108216: Add pycore_dict_struct.h internal header file

[vstinner]

Add a new internal pycore_dict_struct.h header file. It can be used
by debuggers and profilers to inspect a Python dictionary without
having to call Python functions. It should be usable in C++.

pycore_dict.h includes pycore_dict_struct.h (no API change).

• Issue: [C API] The internal C API <pycore_dict.h> cannot be used in C++ #108216

[vstinner]

@P403n1x87: Would you be able to test that Python 3.13 with this change solves your C++ issue?

[vstinner]

cc @methane @serhiy-storchaka

[P403n1x87]

@P403n1x87: Would you be able to test that Python 3.13 with this change solves your C++ issue?

Yep I'll try to test this as soon as I can. If it works, would this be backportable to 3.12?

[vstinner]

Yep I'll try to test this as soon as I can. If it works, would this be backportable to 3.12?

IMO it's way too late to change Python 3.12, since we are close to the release candidate 1.

[P403n1x87]

@vstinner This is looking good https://github.com/P403n1x87/echion/actions/runs/5997599397/job/16264282012 (from PR P403n1x87/echion#9)

[vstinner]

I closed the issue: #108216 (comment)