[JIT] Add `torch._C.ScriptList`` (#52832)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52832
**Summary**
This commit adds `torch._C.ScriptList`, a list type that has reference
semantics across the Python/TorchScript boundary. That is, modifications
made in TorchScript to instances of `torch._C.ScriptList`
are visible in Python even when it is not returned from the function.
`torch._C.ScriptList` is implemented using a modified version of pybind's
`stl_bind.h`-style bindings attached to `ScriptList` and `ScriptListIterator`,
wrapper classes around `c10::impl::GenericList` and
`c10::impl::GenericList::iterator`. These bindings allow instances of
`torch._C.ScriptList` to be used as if it were a
regular `list` in Python. Reference semantics are achieved by simply
retrieving the `IValue` contained in `ScriptList` in `toIValue` (invoked
when converting Python arguments to `IValues` before calling TorchScript
code).
**Test Plan**
This commit adds `TestScriptList` to `test_list_dict.py`, a set of tests
that check that all of the common list operations are supported
and that instances have reference semantics across the
Python/TorchScript boundary.
Test Plan: Imported from OSS
Reviewed By: gmagogsfm
Differential Revision: D29478121
Pulled By: SplitInfinity
fbshipit-source-id: 652cc25cfa37debe28db9527504846f22abd8b54
