Add tests for lower_graph and fix unpack() ops dispatch (#37540)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37540
ghstack-source-id: 103169129
Test Plan:
buck test mode/no-gpu mode/dev //caffe2/test:jit -- 'test_lower_graph_conv \(test_jit\.TestScript\)'
buck test mode/no-gpu mode/dev //caffe2/test:jit -- 'test_lower_graph \(test_jit\.TestScript\)'
Differential Revision: D21313433
fbshipit-source-id: bb9942272784e517b07537ee4c149b9dc4df4c2a
