Boundary CoordinatePosition for Triangle returning incorrect results

[wwaltersdavis]

Currently when getting the coordinate position for some triangle boundary coords, a different CoordPos is returned when using a Triangle vs the same triangle as a Polygon. The Polygon implementation looks to be returning the correct position. This can be created with the following:

use geo::{coord, CoordinatePosition, Polygon, Triangle};

fn triangle_coordpos_error() {
    let p = coord! { x: 10.0, y: 5.0 };

    let triangle: Triangle = Triangle::new(
        coord! { x: 0.0, y: 0.0 },
        coord! { x: 10.0, y: 0.0 },
        coord! { x: 10.0, y: 10.0 },
    );
    let pos_1 = triangle.coordinate_position(&p);

    let triangle_as_polygon: Polygon = triangle.to_polygon();
    let pos_2 = triangle_as_polygon.coordinate_position(&p);

    assert_eq!(pos_1, pos_2);
}

Issue

• Arises when a triangle has one edge which is parallel to the y-axis and the coordinate to get the position of is on that edge.
• Looks to be caused by line 195 where only coords without the same x as the line end.x are accepted as boundary coords.

[wwaltersdavis]

Closes with #1475