Use new API to register custom ExecuTorch kernels into ATen (#2937)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2937

Retry of D55713944
Use `WRAP_TO_ATEN` to register custom ExecuTorch kernel to PyTorch.

This PR added installation logic to `libcustom_ops_aot_lib.so` in `setup.py`. This is to make sure we can build `libcustom_ops_aot_lib.so` and install it to the correct position (`<site-packages>/executorch/examples/models/llama2/custom_ops/libcustom_ops_aot_lib.so`) and then it can be loaded by `torch.ops.load_library`.

Reviewed By: lucylq

Differential Revision: D55907749

fbshipit-source-id: 6b7f9af3c68b31f6df780a041291684eb6ddd90f