[Static Runtime] Support __getitem__ for lists (#63398)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63398
This change provides a native `__getitem__` implementation for lists to avoid overhead associated with falling back to the JIT interpreter.
Test Plan: Unit tests: `buck test //caffe2/benchmarks/static_runtime:static_runtime_cpptest`
Reviewed By: hlu1
Differential Revision: D30368464
fbshipit-source-id: e0e0971508cd5d9bcf6025606993dc24ecbf6764
