Handle private APIs removed in Python 3.13

[osandov]

Fedora reported that drgn fails to build with Python 3.13: https://bugzilla.redhat.com/show_bug.cgi?id=2245652. This is because a few private APIs were removed in Python 3.13.0a1:

• _Py_Identifier and co.: gh-106320: Remove private _Py_Identifier API python/cpython#108593. There appears to have been some discussion about what users should use instead, but nothing definitive.
• _PyLong_FromByteArray() and _PyLong_FromByteArray(): gh-106320: Remove private PyLong C API functions python/cpython#108429. There seems to be some movement to bring those back while a public replacement is designed: gh-106320: Re-add some PyLong/PyDict C-API functions python/cpython#111162.

[osandov]

Most of these removals were reverted. The last two that we still need are _PyDict_GetItemIdWithError() and _PyDict_SetItemId().