fix: Fractional index validation (#11258)

- Vendored fractional-indexing and converted to TypeScript
- Stricter index format validation in fractional-indexing
- Added format validation to fractional index validation

---
Signed-off-by: Mark Tolmacs <mark@lazycat.hu>
Co-authored-by: dwelle <5153846+dwelle@users.noreply.github.com>

packages/excalidraw/package.json

@@ -95,7 +95,6 @@
     "clsx": "1.1.1",
     "cross-env": "7.0.3",
     "es6-promise-pool": "2.5.0",
-    "fractional-indexing": "3.2.0",
     "fuzzy": "0.1.3",
     "image-blob-reduce": "3.0.1",
     "jotai": "2.11.0",