New function Scenic.Script.arc/7 to add arcs to current path

[GPrimola]

Description

This PR adds a new operation arc to add arcs to current path.
This interface is also available on HTML Canvas API: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/arc

Motivation and Context

Today we only have 2 interfaces to have arcs:

• Scenic.Script.draw_arc/4: which draws an arc on a new path;
• Scenic.Script.arc_to/6: which adds an arc on the current path.
  The need for a third arc operation is that none of the above functions provide a flexible interface for arcs as the nvgArc does.

So this new function arc have the same parameters as nvgArc, which gives a more flexible interface for drawing arcs.

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any feature
  but make things better)

Checklist

• Check other PRs and make sure that the changes are not done yet.

Dependencies

This PR depends on changes on https://github.com/ScenicFramework/scenic_driver_local and can only be merged after ScenicFramework/scenic_driver_local#42