Line radius is wrong in 2D views, and has shading

[emilk]

I change the default line radius to 10 points, but the actual radius is around 5 points.
The line is also shaded, which I don't think it should be in 2D views.

Repro:

git checkout 3dc64f9ebb5f04a7e696a4def64b6a66fe7a977d
pixi run rerun

• Open the Human Pose tracking example
• Set default line width for the 2D view to 10 points
• Zoom in and get out your pixel ruler

[Wumpf]

Seems to affect key point connections specifically - I previously tested this with other lines and they were fine, but didn't check on this case!