Add onnx export for floor, ceil, log2 and prim::shape
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/17895
Reviewed By: zrphercule
Differential Revision: D15103396
Pulled By: houseroad
fbshipit-source-id: 2ec80f11a19a8659aa496e68aed769a8dd1efb18
