bpo-32030: Enhance Py_Main() (#4412)

Parse more env vars in Py_Main():

* Add more options to _PyCoreConfig:

  * faulthandler
  * tracemalloc
  * importtime

* Move code to parse environment variables from _Py_InitializeCore()
  to Py_Main(). This change fixes a regression from Python 3.6:
  PYTHONUNBUFFERED is now read before calling pymain_init_stdio().
* _PyFaulthandler_Init() and _PyTraceMalloc_Init() now take an
  argument to decide if the module has to be enabled at startup.
* tracemalloc_start() is now responsible to check the maximum number
  of frames.

Other changes:

* Cleanup Py_Main():

  * Rename some pymain_xxx() subfunctions
  * Add pymain_run_python() subfunction

* Cleanup Py_NewInterpreter()
* _PyInterpreterState_Enable() now reports failure
* init_hash_secret() now considers pyurandom() failure as an "user
  error": don't fail with abort().
* pymain_optlist_append() and pymain_strdup() now sets err on memory
  allocation failure.
diff --git a/Include/internal/pystate.h b/Include/internal/pystate.h
index 516f829..67b4a51 100644
--- a/Include/internal/pystate.h
+++ b/Include/internal/pystate.h
@@ -90,7 +90,7 @@
 
 /* Other */
 
-PyAPI_FUNC(void) _PyInterpreterState_Enable(_PyRuntimeState *);
+PyAPI_FUNC(_PyInitError) _PyInterpreterState_Enable(_PyRuntimeState *);
 
 #ifdef __cplusplus
 }