Aos 2 traits concept efif

[efifogel]

Summary of Changes

This PR does not change the code (except perhaps some negligible changes, such as adding or removing spaces or editing comments).

1. Renamed the prefix of the names of all concepts in the Arrangement_on_surface_2 package from "Arrangement" to "Aos". This slightly affects packages other than the Aos_2 package.
2. Introduced a new concept called AosApproximateTraits_2. It refines the concept AosApproximatePointTraits_2. This concept requires the provision of a functor called Approximate_2. In addition to an operator that approximates the coordinates of a point, it also requires the provision of (i) an operator that approximates a points, and (ii) an operator that approximates a curve.
3. Changed all "typedef" style statements in the user manual to "using" style. (Observe that a similar update to the examples has already been made in a previous release.)

Release Management

• Affected package(s): Arrangement_on_surface_2
• Issue(s) solved (if any): NA
• Feature/Small Feature: Features/Small Features/Aos2 Approximation Concept
• Link to compiled documentation: 2D Arrangement On Surface
• License and copyright ownership: TAU