Multi Point Lines (based on Multi Point Arrows) (#660)

* Enable multi points in lines

* Stop retrieving arrow points for lines

* Migrate lines to new spec during load

* Clean up and refactor some code

- Normalize shape dimensions during load
- Rename getArrowAbsoluteBounds

* Fix linter issues

src/element/handlerRectangles.ts

@@ -1,6 +1,6 @@
 import { ExcalidrawElement } from "./types";
 import { SceneScroll } from "../scene/types";
-import { getArrowAbsoluteBounds } from "./bounds";
+import { getLinearElementAbsoluteBounds } from "./bounds";
 
 type Sides = "n" | "s" | "w" | "e" | "nw" | "ne" | "sw" | "se";
 
@@ -16,10 +16,13 @@ export function handlerRectangles(
   let marginY = -8;
 
   const minimumSize = 40;
-  if (element.type === "arrow") {
-    [elementX1, elementY1, elementX2, elementY2] = getArrowAbsoluteBounds(
-      element,
-    );
+  if (element.type === "arrow" || element.type === "line") {
+    [
+      elementX1,
+      elementY1,
+      elementX2,
+      elementY2,
+    ] = getLinearElementAbsoluteBounds(element);
   } else {
     elementX1 = element.x;
     elementX2 = element.x + element.width;
@@ -90,12 +93,7 @@ export function handlerRectangles(
     8,
   ]; // se
 
-  if (element.type === "line") {
-    return {
-      nw: handlers.nw,
-      se: handlers.se,
-    } as typeof handlers;
-  } else if (element.type === "arrow") {
+  if (element.type === "arrow" || element.type === "line") {
     if (element.points.length === 2) {
       // only check the last point because starting point is always (0,0)
       const [, p1] = element.points;