Improve stroke drawing on 2D collision shapes

[dalexeev]

• Thin lines when scaling CollisionPolygon2D.
• Draw a CollisionPolygon2D stroke on top of the polygon instead of below it.
• Improve the strokes of RectangleShape2D, CircleShape2D, CapsuleShape2D and ConvexPolygonShape2D. Since we can't control the exact position of the thin lines when scaling (and a line of the same color will be drawn next to the shape, not on top of it), I changed the stroke's alpha channel to 1.

Before:

After:

[Calinou]

Drawing the outlines with alpha = 1.0 makes sense to me, looks like improvement.

One reason I made outlines translucent is that you can notice if multiple outlines (from different shapes) are overlapping. It's not essential to do, but it's nice to have to troubleshoot specific issues.

[dalexeev]

I don't insist on alpha = 1.0, but the color of the stroke should be noticeably different from the color of the shape, due to the way drawing lines with width < 0 works.

[akien-mga]

Thanks!