fix: Bounding boxes with rotation exporter to COCO and YOLO

[rgaiacs]

Fixes https://github.com/heartexlabs/label-studio-converter/issues/131

supersedes https://github.com/heartexlabs/label-studio-converter/pull/134

Annotation in Label Studio 1.6.0.rc5 with rotation

COCO exporter bundle with Label Studio 1.6.0.rc5 ignores the rotation

COCO exporter patched with https://github.com/heartexlabs/label-studio-converter/pull/134 after correction is completely wrong

COCO exporter patched with this PR

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@a0595c6). Click here to learn what that means. Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #136 +/- ## ========================================= Coverage ? 21.87% ========================================= Files ? 16 Lines ? 1458 Branches ? 0 ========================================= Hits ? 319 Misses ? 1139 Partials ? 0 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=heartexlabs). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=heartexlabs)

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[rgaiacs]

After fixed calculation of y_0