[3.10] bpo-45467: Fix IncrementalDecoder and StreamReader in the "raw-unicode-escape" codec (GH-28944) (GH-28952)

They support now splitting escape sequences between input chunks.

Add the third parameter "final" in codecs.raw_unicode_escape_decode().
It is True by default to match the former behavior.
(cherry picked from commit 39aa98346d5dd8ac591a7cafb467af21c53f1e5d)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Modules/_codecsmodule.c b/Modules/_codecsmodule.c
index fc74127..50afc09 100644
--- a/Modules/_codecsmodule.c
+++ b/Modules/_codecsmodule.c
@@ -509,17 +509,20 @@ _codecs_unicode_escape_decode_impl(PyObject *module, Py_buffer *data,
 _codecs.raw_unicode_escape_decode
     data: Py_buffer(accept={str, buffer})
     errors: str(accept={str, NoneType}) = None
+    final: bool(accept={int}) = True
     /
 [clinic start generated code]*/
 
 static PyObject *
 _codecs_raw_unicode_escape_decode_impl(PyObject *module, Py_buffer *data,
-                                       const char *errors)
-/*[clinic end generated code: output=c98eeb56028070a6 input=d2f5159ce3b3392f]*/
+                                       const char *errors, int final)
+/*[clinic end generated code: output=11dbd96301e2879e input=2d166191beb3235a]*/
 {
-    PyObject *decoded = PyUnicode_DecodeRawUnicodeEscape(data->buf, data->len,
-                                                         errors);
-    return codec_tuple(decoded, data->len);
+    Py_ssize_t consumed = data->len;
+    PyObject *decoded = _PyUnicode_DecodeRawUnicodeEscapeStateful(data->buf, data->len,
+                                                                  errors,
+                                                                  final ? NULL : &consumed);
+    return codec_tuple(decoded, consumed);
 }
 
 /*[clinic input]