Add support for scene units in the map view

[abey79]

What

• Fixes Assume real-world meters instead of UI unit for "scene unit" Radius values #7872
• Limitation: The scene unit radius of a GeoLineStrings only considers the first vertex' latitude #8013

Add support for scene units (aka meter) in the map view.

map_scene_units.mp4

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[Wumpf]

makes sense!