Wrap internal router state updates with React.startTransition (#10438)

Author: brophdawg11

.changeset/start-transition-support.md

@@ -0,0 +1,6 @@
+---
+"react-router": minor
+"react-router-dom": minor
+---
+
+Wrap internal router state updates with `React.startTransition` if it exists

package.json

@@ -108,16 +108,16 @@
       "none": "45 kB"
     },
     "packages/react-router/dist/react-router.production.min.js": {
-      "none": "13.3 kB"
+      "none": "13.4 kB"
     },
     "packages/react-router/dist/umd/react-router.production.min.js": {
-      "none": "15.6 kB"
+      "none": "15.8 kB"
     },
     "packages/react-router-dom/dist/react-router-dom.production.min.js": {
-      "none": "11.8 kB"
+      "none": "12.0 kB"
     },
     "packages/react-router-dom/dist/umd/react-router-dom.production.min.js": {
-      "none": "17.7 kB"
+      "none": "17.9 kB"
     }
   }
 }

packages/react-router-dom/__tests__/components/LazyComponent.tsx

@@ -0,0 +1,5 @@
+import * as React from "react";
+
+export default function LazyComponent() {
+  return <h1>Lazy</h1>;
+}