Refactor AotCompile to return a pair (#65707)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65707
Refactoring aotCompile to return a pair of compiled function and the LLVM assembly instead of updating an incoming string with assembly code
Testing: Gives expected results when compiled and run
```
(pytorch) ~/local/pytorch refactor_aot
└─ $ build/bin/aot_model_compiler --model mobilenetv3.pt --model_name=pytorch_dev_mobilenetv3 --model_version=v1 --input_dims="2,2,2"
The compiled model was saved to mobilenetv3.compiled.pt
```
Test Plan: Imported from OSS
Reviewed By: qihqi
Differential Revision: D31220452
Pulled By: priyaramani
fbshipit-source-id: f957c53ba83f876a2e7dbdd4b4571a760b3b6a9a
