Merge pull request #27331 from MaximSmolskiy:add-test-for-solveCubic

Add tests for solveCubic #27331

### Pull Request Readiness Checklist

Related to #27323 

I found only randomized tests with number of roots always equal to `1` or `3`, `x^3 = 0` and some simple test for Java and Swift.
Obviously, they don't cover all cases (implementation has strong branching and number of roots can be equal to `-1`, `0` and `2` additionally).
So, I think it will be useful to try explicitly cover more cases (and implementation branches correspondingly)

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] 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
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/core/include/opencv2/core.hpp

@@ -2004,8 +2004,8 @@ The function solveCubic finds the real roots of a cubic equation:
 
 The roots are stored in the roots array.
 @param coeffs equation coefficients, an array of 3 or 4 elements.
-@param roots output array of real roots that has 1 or 3 elements.
-@return number of real roots. It can be 0, 1 or 2.
+@param roots output array of real roots that has 0, 1, 2 or 3 elements.
+@return number of real roots. It can be -1 (all real numbers), 0, 1, 2 or 3.
 */
 CV_EXPORTS_W int solveCubic(InputArray coeffs, OutputArray roots);