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/index.ts

@@ -4,8 +4,7 @@ export {
   getCommonBounds,
   getDiamondPoints,
   getArrowPoints,
-  getLinePoints,
-  getArrowAbsoluteBounds,
+  getLinearElementAbsoluteBounds,
 } from "./bounds";
 
 export { handlerRectangles } from "./handlerRectangles";