Add free draw mode (#1570)

src/element/typeChecks.ts

@@ -14,7 +14,10 @@ export function isLinearElement(
   element?: ExcalidrawElement | null,
 ): element is ExcalidrawLinearElement {
   return (
-    element != null && (element.type === "arrow" || element.type === "line")
+    element != null &&
+    (element.type === "arrow" ||
+      element.type === "line" ||
+      element.type === "draw")
   );
 }
 
@@ -25,6 +28,7 @@ export function isExcalidrawElement(element: any): boolean {
     element?.type === "rectangle" ||
     element?.type === "ellipse" ||
     element?.type === "arrow" ||
+    element?.type === "draw" ||
     element?.type === "line"
   );
 }