feat: support selecting multiple points when editing line (#4373)

src/types.ts

@@ -354,6 +354,7 @@ export type PointerDownState = Readonly<{
     // pointer interaction
     hasBeenDuplicated: boolean;
     hasHitCommonBoundingBoxOfSelectedElements: boolean;
+    hasHitElementInside: boolean;
   };
   withCmdOrCtrl: boolean;
   drag: {
@@ -373,6 +374,9 @@ export type PointerDownState = Readonly<{
     // It's defined on the initial pointer down event
     onKeyUp: null | ((event: KeyboardEvent) => void);
   };
+  boxSelection: {
+    hasOccurred: boolean;
+  };
 }>;
 
 export type ExcalidrawImperativeAPI = {