feat: add line shape (#371)

* feat: add line shape

* fix: align line tool

* fix: hitbox bug sw to ne

* fix: add stroke width n sloppiness  for line

* fix: center line inside a panel box

* fix: use color as a unique key

src/element/bounds.ts

@@ -48,3 +48,12 @@ export function getArrowPoints(element: ExcalidrawElement) {
 
   return [x1, y1, x2, y2, x3, y3, x4, y4];
 }
+
+export function getLinePoints(element: ExcalidrawElement) {
+  const x1 = 0;
+  const y1 = 0;
+  const x2 = element.width;
+  const y2 = element.height;
+
+  return [x1, y1, x2, y2];
+}