[SR] Native implementation for aten::size (#67346)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67346
Native ops are faster than falling back to the JIT interpreter, sometimes significantly (we've previously seen this with ops like TupleUnpack). We should improve op coverage where possible.
Test Plan: `buck test caffe2/benchmarks/static_runtime:static_runtime_cpptest`
Reviewed By: d1jang
Differential Revision: D31965159
fbshipit-source-id: 86a69c395f401c4a4c55daa4c5fe80764383c8e5
