Python 3.12 support

[sbesson]

This is the minimal set of changes required to get a pre-built Ice 3.6.5 wheel packages for Python 3.12.

The primary additional patch is related to the removal of the imp library - see https://docs.python.org/3/whatsnew/3.12.html. A new patch is added similar to zeroc-ice/ice@078cf0b.

The pre-built wheel package has been lightly tested under Ubuntu 23.10 where python3.12 can be installed and the Ice module can be imported minimally

root@eba7bd817e79:/# python3.12 -mvenv venv
root@eba7bd817e79:/# venv/bin/pip install /tmp/zeroc_ice-3.6.5-cp312-cp312-manylinux_2_28_x86_64.whl 
Processing /tmp/zeroc_ice-3.6.5-cp312-cp312-manylinux_2_28_x86_64.whl
Installing collected packages: zeroc-ice
Successfully installed zeroc-ice-3.6.5
root@eba7bd817e79:/# venv/bin/python
Python 3.12.0 (main, Oct  4 2023, 06:27:34) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import Ice
>>>