[RPC] Create local RRef<ModuleInterface> remotely in Python, use it remotely in TorchScript (#34183)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34183
https://github.com/pytorch/pytorch/pull/33263 enhanced the RRef Python constructor to infer most types, by `jit::tryToInferType(..)`.
But this helper function can't infer `ScriptModule` type due to `ScriptModule`'s special per-Module type singleton logic, so it's still not possible for an Python-created RRef to know the JIT type of it's contained `ScriptModule`.
Instead of inferring the specific type of a Module, which could leads to too many candidate types (due to Module's multiple inheritance possibility), it's more straightforward to set it's type as a user-specified `ModuleInterface` type.
We added an optional argument `type_hint` for users to mark an `RRef` for what `ModuleInterface` type it's holds.
ghstack-source-id: 99649379
(Note: this ignores all push blocking failures!)
Test Plan:
Aspects that need to be confirmed in the test cases
https://fb.quip.com/aGxRAh2lCg05
```
buck test mode/dev-nosan //caffe2/test/distributed/rpc/jit:rpc_fork
buck build mode/dev-nosan //caffe2/test/distributed/rpc/jit:rpc_fork \
&& buck-out/gen/caffe2/test/distributed/rpc/jit/rpc_fork\#binary.par -r test_create_local_script_class_rref
buck build mode/dev-nosan //caffe2/test/distributed/rpc/jit:rpc_fork \
&& buck-out/gen/caffe2/test/distributed/rpc/jit/rpc_fork\#binary.par -r test_create_local_script_module_rref
buck build mode/dev-nosan //caffe2/test/distributed/rpc/jit:rpc_fork \
&& buck-out/gen/caffe2/test/distributed/rpc/jit/rpc_fork\#binary.par -r test_return_local_script_class_rref_in_py_and_use_in_script
buck build mode/dev-nosan //caffe2/test/distributed/rpc/jit:rpc_fork \
&& buck-out/gen/caffe2/test/distributed/rpc/jit/rpc_fork\#binary.par -r test_return_local_script_module_rref_in_py_and_use_in_script
buck build mode/dev-nosan //caffe2/test/distributed/rpc/jit:rpc_fork \
&& buck-out/gen/caffe2/test/distributed/rpc/jit/rpc_fork\#binary.par -r test_torchscript_function_exception
```
Differential Revision: D7065050
fbshipit-source-id: e10210c0996622969e499e4a35b0659b36787c1c
