For torch::jit::module's attr method to moble::module (#47059)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47059
This diff adds attr getter to mobile::module similar to torchscript module at https://github.com/pytorch/pytorch/blob/master/torch/csrc/jit/api/object.h#L75-L83.
Test Plan: LiteInterpreterTest::CheckAttrAccess
Reviewed By: xta0
Differential Revision: D24604950
fbshipit-source-id: cfac187f47f5115807dc119fe6c203f60dbd5dff