feat: fractional indexing (#7359)

* Introducing fractional indices as part of `element.index`

* Ensuring invalid fractional indices are always synchronized with the array order

* Simplifying reconciliation based on the fractional indices

* Moving reconciliation inside the `@excalidraw/excalidraw` package

---------

Co-authored-by: Marcel Mraz <marcel@excalidraw.com>
Co-authored-by: dwelle <5153846+dwelle@users.noreply.github.com>

packages/excalidraw/actions/actionHistory.tsx

@@ -10,6 +10,7 @@ import { newElementWith } from "../element/mutateElement";
 import { fixBindingsAfterDeletion } from "../element/binding";
 import { arrayToMap } from "../utils";
 import { isWindows } from "../constants";
+import { syncInvalidIndices } from "../fractionalIndex";
 
 const writeData = (
   prevElements: readonly ExcalidrawElement[],
@@ -48,6 +49,8 @@ const writeData = (
         ),
       );
     fixBindingsAfterDeletion(elements, deletedElements);
+    // TODO: will be replaced in #7348
+    syncInvalidIndices(elements);
 
     return {
       elements,