Added arc_2d function for gizmos

[Kjolnyr]

Objective

Added the possibility to draw arcs in 2d via gizmos

Solution

• Added arc_2d function to Gizmos
• Added arc_inner function
• Added Arc2dBuilder<'a, 's>
• Updated 2d_gizmos.rs example to draw an arc

[Kjolnyr]

@devil-ira can you confirm that my dynamic segment implementation is correct?

[alice-i-cecile]

Left a suggestion for improved docs. Once that's accepted or revised, this LGTM and I'll merge :)

[Kjolnyr]

@alice-i-cecile revision accepted! You doc proposal is much clearer.

My last commit has a change in the code, there was a bug following @devil-ira 's lerp implementation proposal that I didn't catch. It was about DEFAULT_CIRCLE_SEGMENTS being an usize but multiplied with a f32. I don't think this bug fix require a new review though, let me know otherwise.