Method convexity

tests/java/PathTest.java:82–90

()

    public void convexity() {
        try (Path p = new PathBuilder().lineTo(40, 20).lineTo(0, 40).lineTo(0, 0).closePath().build()) {
            assertEquals(true, p.isConvex());
        }

        try (Path p = new PathBuilder().lineTo(40, 40).lineTo(40, 0).lineTo(0, 40).lineTo(0, 0).closePath().build()) {
            assertEquals(false, p.isConvex());
        }
    }

    public void isShape() {
        for (var dir: PathDirection.values()) {