bpo-40268: Rename _PyInterpreterState_GET_UNSAFE() (GH-19509)

Rename _PyInterpreterState_GET_UNSAFE() to _PyInterpreterState_GET()
for consistency with _PyThreadState_GET() and to have a shorter name
(help to fit into 80 columns).

Add also "assert(tstate != NULL);" to the function.
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index 7cb72ce..da04af4 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -6,7 +6,7 @@
 #include "structmember.h"
 #include "pycore_code.h"
 #include "pycore_interp.h"        // PyInterpreterState.co_extra_freefuncs
-#include "pycore_pystate.h"       // _PyInterpreterState_GET_UNSAFE()
+#include "pycore_pystate.h"       // _PyInterpreterState_GET()
 #include "pycore_tupleobject.h"
 #include "clinic/codeobject.c.h"
 
@@ -555,7 +555,7 @@
     co->co_opcache_size = 0;
 
     if (co->co_extra != NULL) {
-        PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+        PyInterpreterState *interp = _PyInterpreterState_GET();
         _PyCodeObjectExtra *co_extra = co->co_extra;
 
         for (Py_ssize_t i = 0; i < co_extra->ce_size; i++) {
@@ -1074,7 +1074,7 @@
 int
 _PyCode_SetExtra(PyObject *code, Py_ssize_t index, void *extra)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
 
     if (!PyCode_Check(code) || index < 0 ||
             index >= interp->co_extra_user_count) {
diff --git a/Objects/moduleobject.c b/Objects/moduleobject.c
index acb920a..1f419ad 100644
--- a/Objects/moduleobject.c
+++ b/Objects/moduleobject.c
@@ -165,7 +165,7 @@
 PyObject *
 PyModule_Create2(struct PyModuleDef* module, int module_api_version)
 {
-    if (!_PyImport_IsInitialized(_PyInterpreterState_GET_UNSAFE())) {
+    if (!_PyImport_IsInitialized(_PyInterpreterState_GET())) {
         PyErr_SetString(PyExc_SystemError,
                         "Python import machinery not initialized");
         return NULL;
@@ -684,7 +684,7 @@
 static PyObject *
 module_repr(PyModuleObject *m)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
 
     return PyObject_CallMethod(interp->importlib, "_module_repr", "O", m);
 }
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 938df24..28ec8f1 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -436,7 +436,7 @@
         return 0;
     }
 
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
 #ifndef Py_DEBUG
     /* In release mode, only check in development mode (-X dev) */
     if (!_PyInterpreterState_GetConfig(interp)->dev_mode) {
@@ -3615,7 +3615,7 @@
 PyObject *
 PyUnicode_EncodeFSDefault(PyObject *unicode)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
     if (interp->fs_codec.utf8) {
         return unicode_encode_utf8(unicode,
                                    interp->fs_codec.error_handler,
@@ -3851,7 +3851,7 @@
 PyObject*
 PyUnicode_DecodeFSDefaultAndSize(const char *s, Py_ssize_t size)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
     if (interp->fs_codec.utf8) {
         return unicode_decode_utf8(s, size,
                                    interp->fs_codec.error_handler,
@@ -16009,7 +16009,7 @@
 int
 _PyUnicode_EnableLegacyWindowsFSEncoding(void)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
     PyConfig *config = (PyConfig *)_PyInterpreterState_GetConfig(interp);
 
     /* Set the filesystem encoding to mbcs/replace (PEP 529) */