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>

scripts/buildUtils.js

@@ -18,6 +18,10 @@ const getConfig = (outdir) => ({
     "@excalidraw/element": path.resolve(__dirname, "../packages/element/src"),
     "@excalidraw/excalidraw": path.resolve(__dirname, "../packages/excalidraw"),
     "@excalidraw/math": path.resolve(__dirname, "../packages/math/src"),
+    "@excalidraw/fractional-indexing": path.resolve(
+      __dirname,
+      "../packages/fractional-indexing/src",
+    ),
     "@excalidraw/utils": path.resolve(__dirname, "../packages/utils/src"),
   },
 });