Add absent skeleton elements automatically in cvat-core

[bsekachev]

Motivation and context

• Add absent skeleton nodes on client to fix error: Edge's nodeFrom ${dataNodeFrom} or nodeTo ${dataNodeTo} do not to refer to any node

• Resolved skeleton editing: right click context menu position wrong in Firefox #6330

• Also fixed invisible menu, like this:

• Added shadow to job item menu:

• Fixed console error (Error: <rect> attribute width: A negative value is not valid. ("-18014398509481942")) on outside skeletons

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)
• I have increased versions of npm packages if it is necessary
  (cvat-canvas,
  cvat-core,
  cvat-data and
  cvat-ui)

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.

[codecov]

Codecov Report

Merging #7302 (23fbecd) into develop (c585209) will decrease coverage by 0.01%.
The diff coverage is 94.44%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7302      +/-   ##
===========================================
- Coverage    82.94%   82.94%   -0.01%     
===========================================
  Files          372      372              
  Lines        39570    39592      +22     
  Branches      3688     3703      +15     
===========================================
+ Hits         32821    32839      +18     
- Misses        6749     6753       +4     

Components	Coverage Δ
cvat-ui	78.39% <94.44%> (-0.01%)	⬇️
cvat-server	87.11% <ø> (+<0.01%)	⬆️