bpo-39947: Use _PyInterpreterState_GET_UNSAFE() (GH-18978)

Replace _PyInterpreterState_Get() function call with
_PyInterpreterState_GET_UNSAFE() macro which is more efficient but
don't check if tstate or interp is NULL.

_Py_GetConfigsAsDict() now uses _PyThreadState_GET().
diff --git a/Objects/moduleobject.c b/Objects/moduleobject.c
index 30de53d..c581951 100644
--- a/Objects/moduleobject.c
+++ b/Objects/moduleobject.c
@@ -174,7 +174,7 @@
 PyObject *
 PyModule_Create2(struct PyModuleDef* module, int module_api_version)
 {
-    if (!_PyImport_IsInitialized(_PyInterpreterState_Get())) {
+    if (!_PyImport_IsInitialized(_PyInterpreterState_GET_UNSAFE())) {
         PyErr_SetString(PyExc_SystemError,
                         "Python import machinery not initialized");
         return NULL;
@@ -699,7 +699,7 @@
 static PyObject *
 module_repr(PyModuleObject *m)
 {
-    PyInterpreterState *interp = _PyInterpreterState_Get();
+    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
 
     return PyObject_CallMethod(interp->importlib, "_module_repr", "O", m);
 }