bpo-43680: _pyio.open() becomes a static method (GH-25354)

The Python _pyio.open() function becomes a static method to behave as
io.open() built-in function: don't become a bound method when stored
as a class variable. It becomes possible since static methods are now
callable in Python 3.10. Moreover, _pyio.OpenWrapper becomes a simple
alias to _pyio.open.

init_set_builtins_open() now sets builtins.open to io.open, rather
than setting it to io.OpenWrapper, since OpenWrapper is now an alias
to open in the io and _pyio modules.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 0ad1796..2dbebe4 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -2241,7 +2241,7 @@ create_stdio(const PyConfig *config, PyObject* io,
     return NULL;
 }
 
-/* Set builtins.open to io.OpenWrapper */
+/* Set builtins.open to io.open */
 static PyStatus
 init_set_builtins_open(void)
 {
@@ -2257,7 +2257,7 @@ init_set_builtins_open(void)
         goto error;
     }
 
-    if (!(wrapper = PyObject_GetAttrString(iomod, "OpenWrapper"))) {
+    if (!(wrapper = PyObject_GetAttrString(iomod, "open"))) {
         goto error;
     }
 
@@ -2279,7 +2279,7 @@ init_set_builtins_open(void)
 }
 
 
-/* Initialize sys.stdin, stdout, stderr and builtins.open */
+/* Create sys.stdin, sys.stdout and sys.stderr */
 static PyStatus
 init_sys_streams(PyThreadState *tstate)
 {