Add more fields to _PyCoreConfig:

* _check_hash_pycs_mode
* bytes_warning
* debug
* inspect
* interactive
* legacy_windows_fs_encoding
* legacy_windows_stdio
* optimization_level
* quiet
* unbuffered_stdio
* user_site_directory
* verbose
* write_bytecode

Changes:

* Remove pymain_get_global_config() and pymain_set_global_config()
  which became useless. These functions have been replaced by
  _PyCoreConfig_GetGlobalConfig() and
  _PyCoreConfig_SetGlobalConfig().
* sys.flags.dont_write_bytecode value is now restricted to 1 even if
  -B option is specified multiple times on the command line.
* PyThreadState_Clear() now uses the config from the current
  interpreter rather than using global Py_VerboseFlag