Add inputsSize to Python IR, like outputsSize

Test Plan:
Used it in some notebooks.

[ghstack-poisoned]

torch/csrc/jit/python/python_ir.cpp

@@ -493,6 +493,7 @@ void initPythonIRBindings(PyObject* module_) {
           })
       .def("sourceRange", [](Node& n) { return n.sourceRange().str(); })
       .def("hasMultipleOutputs", [](Node& n) { return n.outputs().size() > 1; })
+      .def("inputsSize", [](Node& n) { return n.inputs().size(); })
       .def("outputsSize", [](Node& n) { return n.outputs().size(); })
       .NS(kind)
       .def("inputsAt", [](Node& n, size_t i) { return n.inputs().at(i); })