Those functions should not be proposed if they do not compile. We can also remove them from the Vec API (eye might not make sense but ones and zeros do).

This is because there is no way to convert a Matx to Vec, cf: #4650
Adding an explicit constructor does not solve the assignment operator missing and the ambiguities it would create (like how do you convert a Scalar to Vec), except if we create all the possible versions of it.

Pull Request Readiness Checklist

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake