Fix forced copying def_property_readonly for FunctionSchema & friends (pytorch#161301)

This took me a bit to figure out and I'm pretty sure I've looked at
this code before. Pybind uses
`return_value_policy::reference_internal` for `def_property`, which
[causes the owning object to be kept alive for the lifespan of the
return
value](https://pybind11.readthedocs.io/en/stable/advanced/functions.html),
allowing the getter to safely avoid copying the property
value. However, lambdas act like they return `auto`, not
`decltype(auto)`, so our lambdas themselves were forcing copies!

Testing: observed std::vector<Argument> copying disappear in Linux
perf profile of someOpInfo._schema.arguments/returns (in
_python_dispatch.correct_storage_aliasing).

Pull Request resolved: pytorch#161301
Approved by: https://github.com/Skylion007, https://github.com/malfet, https://github.com/wconstab

Author: swolchok

torch/csrc/jit/python/init.cpp

@@ -1958,18 +1958,15 @@ void initJITBindings(PyObject* module) {
            std::vector<Argument>,
            bool,
            bool>())
-      .def_property_readonly(
-          "name", [](const FunctionSchema& self) { return self.name(); })
-      .def_property_readonly(
-          "overload_name",
-          [](const FunctionSchema& self) { return self.overload_name(); })
-      .def_property_readonly(
-          "arguments",
-          [](const FunctionSchema& self) { return self.arguments(); })
-      .def_property_readonly(
-          "returns", [](const FunctionSchema& self) { return self.returns(); })
+      .def_property_readonly("name", &FunctionSchema::name)
+      .def_property_readonly("overload_name", &FunctionSchema::overload_name)
+      .def_property_readonly("arguments", &FunctionSchema::arguments)
+      .def_property_readonly("returns", &FunctionSchema::returns)
       .def(
           "is_backward_compatible_with",
+          // FunctionSchema::isBackwardCompatibleWith has an extra
+          // defaulted argument, so we can't just use a
+          // pointer-to-member here.
           [](const FunctionSchema& self, const FunctionSchema& old_schema) {
             return self.isBackwardCompatibleWith(old_schema);
           })
@@ -2024,12 +2021,9 @@ void initJITBindings(PyObject* module) {
            std::optional<IValue>,
            bool,
            std::optional<AliasInfo>>())
-      .def_property_readonly(
-          "name", [](const Argument& self) { return self.name(); })
-      .def_property_readonly(
-          "type", [](const Argument& self) { return self.type(); })
-      .def_property_readonly(
-          "real_type", [](const Argument& self) { return self.real_type(); })
+      .def_property_readonly("name", &Argument::name)
+      .def_property_readonly("type", &Argument::type)
+      .def_property_readonly("real_type", &Argument::real_type)
       .def_property_readonly(
           "N",
           [](const Argument& self) -> py::object {