Scatterplotgraph: Implement manual repositioning of points

[janezd]

Description of changes

Implement moving of points (a single point or selection) by dragging them.

The functionality is enabled if the widget (not graph!) implements a method set_coordinates.

I don't know how to write reasonable tests for this. Test on biolab/orange3-network#293.

This functionality would also be useful for other widgets that position points using some local optimization, for instance MDS, tSNE, FreeViz.

Includes

• Code changes
• Tests
• Documentation

[Copilot]

Pull request overview

Adds support for manually repositioning points in scatterplot-based visualizations by dragging (single point or current selection), gated by the widget providing a set_coordinates hook.

Changes:

• Extend InteractiveViewBox.mouseDragEvent to detect draggable points and apply a drag delta during mouse drags.
• Add get_dragged_points / move_dragged_points to OWScatterPlotBase to support dragging a point or the full current selection.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
Orange/widgets/visualize/utils/plotutils.py	Adds drag-handling branch to InteractiveViewBox.mouseDragEvent to initiate/track point dragging.
Orange/widgets/visualize/owscatterplotgraph.py	Implements scatterplot-specific point hit-testing and coordinate updates via set_coordinates.

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[codecov]

Codecov Report

❌ Patch coverage is 12.90323% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.00%. Comparing base (f12c5c1) to head (072b16a).
⚠️ Report is 8 commits behind head on master.

❌ Your patch check has failed because the patch coverage (12.90%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7286      +/-   ##
==========================================
- Coverage   89.01%   89.00%   -0.02%     
==========================================
  Files         336      336              
  Lines       74417    74464      +47     
==========================================
+ Hits        66242    66275      +33     
- Misses       8175     8189      +14     

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