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/buildBase.js

@@ -13,7 +13,12 @@ const getConfig = (outdir) => ({
   alias: {
     "@excalidraw/utils": path.resolve(__dirname, "../packages/utils/src"),
   },
-  external: ["@excalidraw/common", "@excalidraw/element", "@excalidraw/math"],
+  external: [
+    "@excalidraw/common",
+    "@excalidraw/element",
+    "@excalidraw/math",
+    "@excalidraw/fractional-indexing",
+  ],
 });
 
 function buildDev(config) {