Real mid and more

[jamesbradleym]

BACKGROUND:

• In our transition to 2.0 much of our curve behavior changes in lieu of their parameterization, here we introduce a new interface IHasArcLength which enforces Midpoint(), PointAtLength(), PointAtNormalizedLength(), and DivideByLength() which applies to Circles, Lines, Polylines, and Beziers.
• Additionally Bezier felt unloved given the push to supporting curves, to perk it up we introduce Split functionality and normalized parameterization + parameter at functionality, and Bezier.ConstructPiecewiseCubicBezier()

DESCRIPTION:

• Gives Circles, Lines, Polylines, and Beziers more flexibility in the information they can return.

TESTING:

• Play around with Circles, Lines, Polylines, and Beziers looking at Midpoint(), PointAtLength(), PointAtNormalizedLength(), and DivideByLength() and for Bezier poke around ParameterAt(), PointAtNormalized() Building multi point Bezier.ConstructPiecewiseCubicBezier(), dividing Beziers, spliting Beziers.

FUTURE WORK:

• Is there any future work needed or anticipated? Does this PR create any obvious technical debt?

REQUIRED:

• [x] All changes are up to date in CHANGELOG.md.

COMMENTS:

• Any other notes.

---

This change is 

[ikeough]

A couple of high level comments. I'm moving this out to 2.1 for further design. Much of what is in here should be, if we choose to bring it in, part of the IBoundedCurve interface, which is the base interface for all bounded curves. Circle is not a bounded curve, so it should not have an arc length. However, Arc which is a trimmed curve with a Circle for its basis curve should have an arc length. As should EllipticalArc. We can discuss more when 2.0 is out the door.