[3.8] bpo-38234: Fix PyConfig_Read() when Py_SetPath() was called (GH-16298) (GH...

[3.8] bpo-38234: Fix PyConfig_Read() when Py_SetPath() was called (GH-16298) (GH-16313)

* bpo-38234: Remove _PyPathConfig.dll_path (GH-16307)

The DLL path is not computed from any user configuration and cannot
be configured by PyConfig. Instead, add a new _Py_dll_path global variable.

Remove _PyConfig_SetPathConfig(): replaced with _PyPathConfig_Init().

Py_Initialize() now longer sets the "global path configuration",
but only initialize _Py_dll_path.

(cherry picked from commit c422167749f92d4170203e996a2c619c818335ea)

* bpo-38234: Fix PyConfig_Read() when Py_SetPath() was called (GH-16298)

* If Py_SetPath() has been called, _PyConfig_InitPathConfig() now
  uses its value.
* Py_Initialize() now longer copies path configuration from PyConfig
  to the global path configuration (_Py_path_config).

(cherry picked from commit e267793aa4101b2771ed0e66aaff5743d23f59af)