gh-117764: Add signatures for some objects in the itertools module (G…

…H-117774)

Modules/itertoolsmodule.c

@@ -2189,7 +2189,8 @@ chain_setstate(chainobject *lz, PyObject *state)
 }
 
 PyDoc_STRVAR(chain_doc,
-"chain(*iterables) --> chain object\n\
+"chain(*iterables)\n\
+--\n\
 \n\
 Return a chain object whose .__next__() method returns elements from the\n\
 first iterable until it is exhausted, then elements from the next\n\
@@ -2528,7 +2529,8 @@ static PyMethodDef product_methods[] = {
 };
 
 PyDoc_STRVAR(product_doc,
-"product(*iterables, repeat=1) --> product object\n\
+"product(*iterables, repeat=1)\n\
+--\n\
 \n\
 Cartesian product of input iterables.  Equivalent to nested for-loops.\n\n\
 For example, product(A, B) returns the same as:  ((x,y) for x in A for y in B).\n\
@@ -4573,7 +4575,8 @@ static PyMethodDef zip_longest_methods[] = {
 };
 
 PyDoc_STRVAR(zip_longest_doc,
-"zip_longest(iter1 [,iter2 [...]], [fillvalue=None]) --> zip_longest object\n\
+"zip_longest(*iterables, fillvalue=None)\n\
+--\n\
 \n\
 Return a zip_longest object whose .__next__() method returns a tuple where\n\
 the i-th element comes from the i-th iterable argument.  The .__next__()\n\