Add CastLike grad

[youzow3]

Description

Add CastLike grad implementation.

Motivation and Context

Some models use CastLike instead of Cast, which prevents on-device training artifacts from being generated.

[youzow3]

@microsoft-github-policy-service agree

[snnn]

Thanks for adding the gradient for CastLike! The implementation looks correct.

I have one suggestion regarding the test:

The new test CastLikeGrad is a good starting point. As the TODO comment mentions, it would be great to add more test cases to cover various type combinations, similar to the existing CastGrad test. This would ensure that the gradient calculation is correct when casting between different data types (e.g., float to double, float to int32, etc.).

Other than that, the changes look good to me.

[youzow3]

Updated the test code but I'm not sure this is correct code to test cast between float-double.
Also, I think integer types cannot have gradient and gradient for "target_type" is always 0, so I don't think we need tests for cast between integer to float or float to integer.