[Enhancement] Give the meaning of Calculation formula to draw line, or object

[1chooo]

Take Generalization Line as an example, the current "calculation formula" containing in the draw(); however, at the first glance, we cannot identify what this calculation formula doing; therefore, we can wrap them as the function to be called by draw().

uml-editor/src/Shapes/GeneralizationLine.java

Lines 14 to 37 in f196072

	// TODO: Change the arrow to hollow (outline), ensuring the line does not pass through the arrow.
	public void draw(Graphics g) {
	int width = 10, height = 10;
	int dx = x2 - x1, dy = y2 - y1;
	double D = Math.sqrt(dx * dx + dy * dy);
	double xm = D - width, xn = xm;
	double ym = height, yn = -height;
	double x;
	double sin = dy / D, cos = dx / D;
	x = xm * cos - ym * sin + x1;
	ym = xm * sin + ym * cos + y1;
	xm = x;
	x = xn * cos - yn * sin + x1;
	yn = xn * sin + yn * cos + y1;
	xn = x;
	int[] xpoints = { x2, (int) xm, (int) xn };
	int[] ypoints = { y2, (int) ym, (int) yn };
	g.drawLine(x1, y1, x2, y2);
	g.drawPolygon(xpoints, ypoints, 3);
	}

related: #11