Fix periodic debug tests failing due to FakeProcessGroup things (pytorch#165479)

These happen when building with CMAKE_BUILD_TYPE=RelWithAssert

This should fix two types of failures that started with pytorch#163665

Disclaimer that I used a lot of AI since I don't how pybind works or what refcounts and pointers are, so idk if this is a good solution, or even a solution at all (fwiw the tests pass now)

The first one type is

Truncated:
```
    default_pg, _ = _new_process_group_helper(
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/distributed/distributed_c10d.py", line 2096, in _new_process_group_helper
    backend_class = creator_fn(dist_backend_opts, backend_options)
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_internal/distributed/fake_pg.py", line 25, in _create_fake_pg
    return FakeProcessGroup._create_internal(
RuntimeError: new_refcount != 1 INTERNAL ASSERT FAILED at "/var/lib/jenkins/workspace/c10/util/intrusive_ptr.h":319, please report a bug to PyTorch. intrusive_ptr: Cannot increase refcount after it reached zero.
Exception raised from retain_ at /var/lib/jenkins/workspace/c10/util/intrusive_ptr.h:319 (most recent call first):
C++ CapturedTraceback:
#4 std::_Function_handler<std::shared_ptr<c10::LazyValue<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > const> (), c10::SetStackTraceFetcher(std::function<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > ()>)::{lambda()#1}>::_M_invoke(std::_Any_data const&) from Logging.cpp:0
#5 c10::Error::Error(c10::SourceLocation, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >) from ??:0
#6 c10::detail::torchCheckFail(char const*, char const*, unsigned int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) from ??:0
#7 c10::detail::torchInternalAssertFail(char const*, char const*, unsigned int, char const*, char const*) from ??:0
#8 void pybind11::class_<c10d::FakeProcessGroup, (anonymous namespace)::IntrusivePtrNoGilDestructor<c10d::FakeProcessGroup> >::init_instance<(anonymous namespace)::IntrusivePtrNoGilDestructor<c10d::FakeProcessGroup>, 0>(pybind11::detail::instance*, void const*) from init.cpp:0
#9 pybind11::detail::type_caster_generic::cast(void const*, pybind11::return_value_policy, pybind11::handle, pybind11::detail::type_info const*, void* (*)(void const*), void* (*)(void const*), void const*) from :0
#10 pybind11::cpp_function::initialize<torch::distributed::c10d::(anonymous namespace)::c10d_init(_object*, _object*)::{lambda(int, int, c10::intrusive_ptr<c10d::FakeProcessGroup::Options, c10::detail::intrusive_target_default_null_type<c10d::FakeProcessGroup::Options> >)pytorch#127}, c10::intrusive_ptr<c10d::FakeProcessGroup, c10::detail::intrusive_target_default_null_type<c10d::FakeProcessGroup> >, int, int, c10::intrusive_ptr<c10d::FakeProcessGroup::Options, c10::detail::intrusive_target_default_null_type<c10d::FakeProcessGroup::Options> >, pybind11::name, pybind11::scope, pybind11::sibling, pybind11::arg, pybind11::arg, pybind11::arg_v>(torch::distributed::c10d::(anonymous namespace)::c10d_init(_object*, _object*)::{lambda(int, int, c10::intrusive_ptr<c10d::FakeProcessGroup::Options, c10::detail::intrusive_target_default_null_type<c10d::FakeProcessGroup::Options> >)pytorch#127}&&, c10::intrusive_ptr<c10d::FakeProcessGroup, c10::detail::intrusive_target_default_null_type<c10d::FakeProcessGroup> > (*)(int, int, c10::intrusive_ptr<c10d::FakeProcessGroup::Options, c10::detail::intrusive_target_default_null_type<c10d::FakeProcessGroup::Options> >), pybind11::name const&, pybind11::scope const&, pybind11::sibling const&, pybind11::arg const&, pybind11::arg const&, pybind11::arg_v const&)::{lambda(pybind11::detail::function_call&)#3}::_FUN(pybind11::detail::function_call&) from init.cpp:0
```
and I fix it here by getting rid of `DontIncreaseRefcount` and using make_intrusive to do the ref count handling instead.  However, I also had to move the constructor to be public, which I think is not good, based on the reasoning of the original PR

The other one type is
```
Traceback (most recent call last):
  File "/var/lib/jenkins/workspace/test/test_testing.py", line 2415, in test_no_warning_on_import
    self.assertEqual(out, "")
  File "/opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/testing/_internal/common_utils.py", line 4233, in assertEqual
    raise error_metas.pop()[0].to_error(  # type: ignore[index]
AssertionError: String comparison failed: "/opt/conda/envs/py_3.10/lib/python3.10/s[352 chars]):\n" != ''
- /opt/conda/envs/py_3.10/lib/python3.10/site-packages/torch/distributed/__init__.py:29: FutureWarning: pybind11-bound class 'torch._C._distributed_c10d.FakeProcessGroup' is using an old-style placement-new '__init__' which has been deprecated. See the upgrade guide in pybind11's docs. This message is only visible when compiled in debug mode.
-   if is_available() and not torch._C._c10d_init():

To execute this test, run the following from the base repo dir:
    python test/test_testing.py TestImports.test_no_warning_on_import
```
which I fix by getting rid of the `__init__` which I think is ok since it'll just error if you try to make one?

Pull Request resolved: pytorch#165479
Approved by: https://github.com/ezyang

Author: clee2000

test/distributed/test_fake_pg.py

@@ -273,12 +273,7 @@ def __torch_dispatch__(self, func, types, args=(), kwargs=None):
                     kwargs = {}
                 return func(*args, **kwargs)
 
-        with self.assertRaisesRegex(
-            RuntimeError,
-            r"FakeProcessGroup cannot be constructed directly\. "
-            r"Use torch\.distributed\.init_process_group\(backend='fake'\) instead to ensure "
-            r"proper dispatch system integration\.",
-        ):
+        with self.assertRaisesRegex(TypeError, r"No constructor defined"):
             fake_pg = FakeProcessGroup(rank=0, world_size=3)
 
             with SimpleTensorMode():

torch/_C/_distributed_c10d.pyi

@@ -607,7 +607,6 @@ class ProcessGroup:
     def group_desc(self) -> str: ...
 
 class FakeProcessGroup(Backend):
-    def __init__(self, rank: int, world_size: int) -> None: ...
     @staticmethod
     def _create_internal(rank: int, world_size: int) -> FakeProcessGroup: ...
 

torch/csrc/distributed/c10d/FakeProcessGroup.hpp

@@ -33,9 +33,8 @@ class FakeProcessGroup : public Backend {
       int rank,
       int size,
       c10::intrusive_ptr<Options> options = c10::make_intrusive<Options>()) {
-    return c10::intrusive_ptr<FakeProcessGroup>(
-        new FakeProcessGroup(rank, size, std::move(options)),
-        c10::raw::DontIncreaseRefcount{});
+    return c10::make_intrusive<FakeProcessGroup>(
+        rank, size, std::move(options));
   }
 
   const std::string getBackendName() const override {
@@ -238,12 +237,12 @@ class FakeProcessGroup : public Backend {
     return c10::make_intrusive<FakeWork>();
   }
 
- private:
   // Private constructor used by official APIs
   FakeProcessGroup(int rank, int size, c10::intrusive_ptr<Options> options)
       : Backend(rank, size), options_(std::move(options)) {}
   c10::intrusive_ptr<Options> options_;
 
+ private:
   void checkCollectiveError() {
     TORCH_CHECK(
         !options_ || !options_->error_on_collective,

torch/csrc/distributed/c10d/init.cpp

@@ -3862,17 +3862,6 @@ such as `dist.all_reduce(tensor, async_op=True)`.
           py::arg("world_size"),
           py::arg("options") =
               c10::make_intrusive<::c10d::FakeProcessGroup::Options>())
-      .def(
-          "__init__",
-          [](const py::object&,
-             const py::args& args,
-             const py::kwargs& kwargs) {
-            TORCH_CHECK(
-                false,
-                "FakeProcessGroup cannot be constructed directly. "
-                "Use torch.distributed.init_process_group(backend='fake') instead to ensure "
-                "proper dispatch system integration.");
-          })
       .def_property_readonly(
           "options", &::c10d::FakeProcessGroup::getBackendOptions);
   auto fakeWork =