Backport 'Fix ctypes structs' (97702) to 3.11

[matthiasgoergens]

Mostly for testing against libraries like numpy. I am not sure whether it will make sense to actually release the backport, as it breaks bug-for-bug compatibility. See #97702 for the discussion.

• Issue: ctypes: bit field data does not survive round trip #97588

• Issue: ctypes: bitfield lost data with union on linux platform #95496

• Issue: bitfield layout wrong in ctypes #84039

• Issue: [Linux] ctypes packs bitfields Incorrectly #73939

• Issue: ctypes mixed-types bitfield layout nonsensical; doesn't match compiler. #59324

• Issue: Incorrect struct definition with bitfields #86098

[hugovk]

@matthiasgoergens Hi! I'm going to close this PR because it's targeting the 3.11 branch, which is now accepting security fixes only: https://devguide.python.org/versions/

Do you still need it for testing? We can re-open if so, or you can also open against your own fork.

[matthiasgoergens]

Please feel free to leave this closed.

Thanks for doing the cleanup!