bpo-43268: Pass interp rather than tstate to internal functions (GH-24580)

Pass the current interpreter (interp) rather than the current Python
thread state (tstate) to internal functions which only use the
interpreter.

Modified functions:

* _PyXXX_Fini() and _PyXXX_ClearFreeList() functions
* _PyEval_SignalAsyncExc(), make_pending_calls()
* _PySys_GetObject(), sys_set_object(), sys_set_object_id(), sys_set_object_str()
* should_audit(), set_flags_from_config(), make_flags()
* _PyAtExit_Call()
* init_stdio_encoding()
* etc.
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 34fb57a..fdeb189 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -2026,9 +2026,9 @@ _PyFloat_Init(void)
 }
 
 void
-_PyFloat_ClearFreeList(PyThreadState *tstate)
+_PyFloat_ClearFreeList(PyInterpreterState *interp)
 {
-    struct _Py_float_state *state = &tstate->interp->float_state;
+    struct _Py_float_state *state = &interp->float_state;
     PyFloatObject *f = state->free_list;
     while (f != NULL) {
         PyFloatObject *next = (PyFloatObject*) Py_TYPE(f);
@@ -2040,11 +2040,11 @@ _PyFloat_ClearFreeList(PyThreadState *tstate)
 }
 
 void
-_PyFloat_Fini(PyThreadState *tstate)
+_PyFloat_Fini(PyInterpreterState *interp)
 {
-    _PyFloat_ClearFreeList(tstate);
+    _PyFloat_ClearFreeList(interp);
 #ifdef Py_DEBUG
-    struct _Py_float_state *state = &tstate->interp->float_state;
+    struct _Py_float_state *state = &interp->float_state;
     state->numfree = -1;
 #endif
 }