Gizmos: arc_2d utility helpers

[RobWalt]

Objective

Since #14731 is merged, it unblocked a few utility methods for 2D arcs. In 2D the pendant to long_arc_3d_between and short_arc_3d_between are missing. Since arc_2d can be a bit hard to use, this PR is trying to plug some holes in the arcs API.

Solution

Implement

• long_arc_2d_between(center, from, tp, color)
• short_arc_2d_between(center, from, tp, color)

Testing

• There are new doc tests
• The 2d_gizmos example has been extended a bit to include a few more arcs which can easily be checked with respect to the grid

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Showcase

Code related to the screenshot (from outer = first line to inner = last line)

    my_gizmos.arc_2d(Isometry2d::IDENTITY, FRAC_PI_2, 80.0, ORANGE_RED);
    my_gizmos.short_arc_2d_between(Vec2::ZERO, Vec2::X * 40.0, Vec2::Y * 40.0, ORANGE_RED);
    my_gizmos.long_arc_2d_between(Vec2::ZERO, Vec2::X * 20.0, Vec2::Y * 20.0, ORANGE_RED);

[bushrat011899]

Looks good, excellent documentation!

[alice-i-cecile]

Merge conflicting with #14676 now, sorry!

[RobWalt]

Merge conflicting with #14676 now, sorry!

No worries, not a problem at all! 💚

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Oops just now noticed that the showcase example posted didn't really do what the code said. Updated it now

Before

After

Code

    my_gizmos.arc_2d(Isometry2d::IDENTITY, FRAC_PI_2, 80.0, ORANGE_RED);
    my_gizmos.short_arc_2d_between(Vec2::ZERO, Vec2::X * 40.0, Vec2::Y * 40.0, ORANGE_RED);
    my_gizmos.long_arc_2d_between(Vec2::ZERO, Vec2::X * 20.0, Vec2::Y * 20.0, ORANGE_RED);