bpo-39245: Switch to public API for Vectorcall (GH-18460)

The bulk of this patch was generated automatically with:

    for name in \
        PyObject_Vectorcall \
        Py_TPFLAGS_HAVE_VECTORCALL \
        PyObject_VectorcallMethod \
        PyVectorcall_Function \
        PyObject_CallOneArg \
        PyObject_CallMethodNoArgs \
        PyObject_CallMethodOneArg \
    ;
    do
        echo $name
        git grep -lwz _$name | xargs -0 sed -i "s/\b_$name\b/$name/g"
    done

    old=_PyObject_FastCallDict
    new=PyObject_VectorcallDict
    git grep -lwz $old | xargs -0 sed -i "s/\b$old\b/$new/g"

and then cleaned up:

- Revert changes to in docs & news
- Revert changes to backcompat defines in headers
- Nudge misaligned comments
diff --git a/Modules/_sqlite/microprotocols.c b/Modules/_sqlite/microprotocols.c
index bdcb174..bb0d19f 100644
--- a/Modules/_sqlite/microprotocols.c
+++ b/Modules/_sqlite/microprotocols.c
@@ -92,7 +92,7 @@
     Py_DECREF(key);
     if (adapter) {
         Py_INCREF(adapter);
-        adapted = _PyObject_CallOneArg(adapter, obj);
+        adapted = PyObject_CallOneArg(adapter, obj);
         Py_DECREF(adapter);
         return adapted;
     }
@@ -105,7 +105,7 @@
         return NULL;
     }
     if (adapter) {
-        adapted = _PyObject_CallOneArg(adapter, obj);
+        adapted = PyObject_CallOneArg(adapter, obj);
         Py_DECREF(adapter);
 
         if (adapted == Py_None) {
@@ -124,7 +124,7 @@
         return NULL;
     }
     if (adapter) {
-        adapted = _PyObject_CallOneArg(adapter, proto);
+        adapted = PyObject_CallOneArg(adapter, proto);
         Py_DECREF(adapter);
 
         if (adapted == Py_None) {