Added ArcTan2 operation

[yrahul3910]

Proposed changes

This PR adds the arctan2 operation, as discussed in #1065.

Checklist

Put an x in the boxes that apply.

• [x] I have read the CONTRIBUTING document
• [x] I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have updated the necessary documentation (if needed)

[yrahul3910]

Thanks! Is that linux build supposed to pass? It seems like it's mainly having trouble finding the ArcTan2 symbol and I'm not sure what I missed.

[awni]

Yes, linux tests should pass. I think you just need to add to the list here: https://github.com/ml-explore/mlx/blob/main/mlx/backend/common/default_primitives.cpp#L36

That is just a way of saying that we should just use the default eval when accelerate is not available (e.g. on linux).