bpo-36301: Add _Py_PreInitializeFromConfig() (GH-12536)

* Initialize _PyPreConfig.dev_mode to -1.
* _PyPreConfig_Read(): coreconfig has the priority over preconfig.
* _PyCoreConfig_Read() now calls _PyPreCmdline_Read() internally.
* config_from_cmdline() now pass _PyPreCmdline to config_read().
* Add _PyPreCmdline_Copy().
diff --git a/Include/cpython/coreconfig.h b/Include/cpython/coreconfig.h
index 8362209..bb086cb 100644
--- a/Include/cpython/coreconfig.h
+++ b/Include/cpython/coreconfig.h
@@ -115,7 +115,9 @@
         .isolated = -1, \
         .use_environment = -1, \
         .coerce_c_locale = -1, \
-        .utf8_mode = -1}
+        .utf8_mode = -1, \
+        .dev_mode = -1, \
+        .allocator = NULL}
 
 
 /* --- _PyCoreConfig ---------------------------------------------- */
diff --git a/Include/cpython/pylifecycle.h b/Include/cpython/pylifecycle.h
index 1caeb98..a226de8 100644
--- a/Include/cpython/pylifecycle.h
+++ b/Include/cpython/pylifecycle.h
@@ -17,6 +17,8 @@
 PyAPI_FUNC(_PyInitError) _Py_PreInitialize(void);
 PyAPI_FUNC(_PyInitError) _Py_PreInitializeFromPreConfig(
     _PyPreConfig *preconfig);
+PyAPI_FUNC(_PyInitError) _Py_PreInitializeFromConfig(
+    const _PyCoreConfig *coreconfig);
 
 PyAPI_FUNC(_PyInitError) _Py_InitializeCore(
     PyInterpreterState **interp,