The improvements are done to `ViewProviderWire` which propagates
to many objects like Line, Wire (polyline), BSpline, BezCurve,
Fillet, etc.
The initialization of the properties is moved to a method
`_set_properties`. The properties `EndArrow`, `ArrowSize`,
`ArrowType` are created only if they do not exist.
This allows calling `ViewProviderWire(obj.ViewObject)`
to migrate an older object to this viewprovider
but without adding duplicated properties.
In particular, this is done to support the migration of the older
`Fillet` object.
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