Support importing and exporting of masks with holes

[zhiltsov-max]

A way to do it is to use polygon hierarchy from cv.findContours of check polygon curve orientation.

Related https://github.com/openvinotoolkit/cvat/issues/2958 Related https://github.com/openvinotoolkit/cvat/issues/1849 Related https://github.com/openvinotoolkit/cvat/issues/2381 Related https://github.com/openvinotoolkit/cvat/issues/2384 Related https://github.com/openvinotoolkit/cvat/issues/2385 Related https://github.com/openvinotoolkit/cvat/issues/2745

[macimovic]

Any update on this? This is very useful for my use case.

[zhiltsov-max]

@macimovic, hi, could you share your use case? If you're interested about CVAT, we've already implemented a way to export masks with holes. For further extension of this functionality, we need better understanding of how it should be designed.