SelectionBox: Fixed the offset on the selection box highlight appearing in the Graph Editor when dragging to select Nodes

[waaake]

Description

This PR addresses an issue with the offset during clicking and dragging on the Graph Editor to invoke the selection box for selecting Edges.
As seen in many cases, the selection box bounds have an offset from the current position of the mouse and this offset remains consistent when moving from left to right and then right to left, causing the user some difficulty in precision of the Selection.

Features list

• Fix Selection Offset for Selection Box.

Implementation remarks

The mouseArea's drag.smoothed attribute controls when the target moves to the mouse position, setting the value as true which is default makes the target move only after the drag has started causing a slight offset which is noticable.
Whereas setting the property to be false ensures that the target will be moved straight to the current mouse position.

The proposed implementation considers and saves the existing value of the drag.smoothed property, sets the value of the property as false when the selection starts and upon selection end, the drag.smoothed property is restored to the original value.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.93%. Comparing base (3e8b736) to head (bf857bc).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2647   +/-   ##
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  Coverage    69.93%   69.93%           
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  Files          121      121           
  Lines         7088     7088           
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  Hits          4957     4957           
  Misses        2131     2131           

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