Add Rounded box gizmos

[lynn-lumen]

Objective

• Implement rounded cuboids and rectangles, suggestion of #9400

Solution

• Added Gizmos::rounded_cuboid, Gizmos::rounded_rect and Gizmos::rounded_rect_2d.
• All of these return builders that allow configuring of the corner/edge radius using .corner_radius(...) or .edge_radius(...) as well as the line segments of each arc using .arc_segments(...).

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Changelog

• Added a new rounded_box module to bevy_gizmos containing all of the above methods and builders.
• Updated the examples 2d_gizmos and 3d_gizmos

Additional information

The 3d example now looks like this:

And this is the updated 2d example showcasing negative corner radius: