bpo-31650, bpo-34170: Replace _Py_CheckHashBasedPycsMode with
_PyCoreConfig._check_hash_pycs_mode. Modify PyInit__imp() and
zipimport to get the parameter from the current interpreter core
configuration.

Remove Include/internal/import.h file.

* Add Include/coreconfig.h
* Move config_*() and _PyCoreConfig_*() functions from Modules/main.c
  to a new Python/coreconfig.c file.
* Inline _Py_ReadHashSeed() into config_init_hash_seed()
* Move global configuration variables to coreconfig.c