Fixed dragging method for skeletons

[bsekachev]

Motivation and context

As skeletons implemented via groups, current approach does not work for them. Thus shape.x(), or shape.y() are always zero.

The SVGGraphicsElement.getBBox() or (bbox() in context of svg.js) method allows us to determine the coordinates of the smallest rectangle in which the object fits. The coordinates returned are with respect to the current SVG space (after the application of all geometry attributes on all the elements contained in the target element).

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (see GitHub docs)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.85%. Comparing base (5d69c7e) to head (37063a8).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8976      +/-   ##
===========================================
- Coverage    73.85%   73.85%   -0.01%     
===========================================
  Files          417      417              
  Lines        44590    44591       +1     
  Branches      4031     4031              
===========================================
- Hits         32932    32931       -1     
- Misses       11658    11660       +2     

Components	Coverage Δ
cvat-ui	78.30% <100.00%> (-0.01%)	⬇️
cvat-server	70.06% <ø> (ø)