Add ICoordinate2D, IVector2D, IMatrix2D

[lysz210]

Declaring basic Interfaces with only properties can help passing plain object to method.

interface ICoordinate2D { x:number; y:number }
class Point2D extends ICoordinate2D {
...
  add(that: ICoordinate2D)
...
}

In the example add can be called with a plain object that has an x and y properties that are numbers.
with add(that: Point2D) the method must be called with a Point2D or an object that has x and y as number and all the methods in Point2D class and you're forced to call add(new Point(1,1)) instead of add({x: 1, y: 1}).
A practical use-case with object destructuring:

const el = document.querySelector('#the-div')
const myPoint = new Point()
el.addEventListener('mousemove', ({clientX: x = 0, clientY: y = 0}) => {
  myPoint = myPoint.add({x, y})
})

The IVector2D can be a alias of ICoordinate2D this can allow to:

interface IVector2D extends ICoordinate2D {}
class Vector2D extends IVector2D {
...
}
// this with allow to use Point2D with a Vector
// I'm not sure about this, if can be considered correct.
Vector2D v = new Vector2D(1,2)
Point2D p = new Point2D(1,1)
Point2D p2 = p.add(v) // this doesn't rais any warnings/errors becaus Vector2D is subclass of Vector2D and has numeric properties x and y