[PyTorch] Lite interpreter with a backend delegate (#54462)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54462
Unclean files during sync - Sat Mar 20 04:00:02 PDT 2021
Unclean files during sync - Sun Mar 21 04:00:01 PDT 2021
ghstack-source-id: 124585992
Test Plan:
```
buck run xplat/caffe2/fb/test/delegate:interpreter_test -- --model_file_path=/path/to/mobile_model.ptl
```
Reviewed By: raziel
Differential Revision: D27232309
fbshipit-source-id: 8504a3185339d73bfa6e924485c4745acf269cec
