fix(react-router): fix transitions (#2969)

* fix(react-router): fix transitions

fixes #2631
fixes #2082

* ci: apply automated fixes

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

Author: schiller-manuel

packages/react-router/src/Transitioner.tsx

@@ -11,7 +11,7 @@ export function Transitioner() {
     select: ({ isLoading }) => isLoading,
   })
 
-  const [isTransitioning, startReactTransition_] = React.useTransition()
+  const [isTransitioning, setIsTransitioning] = React.useState(false)
   // Track pending state changes
   const hasPendingMatches = useRouterState({
     select: (s) => s.matches.some((d) => d.status === 'pending'),
@@ -27,7 +27,13 @@ export function Transitioner() {
   const previousIsPagePending = usePrevious(isPagePending)
 
   if (!router.isServer) {
-    router.startReactTransition = startReactTransition_
+    router.startReactTransition = (fn: () => void) => {
+      setIsTransitioning(true)
+      React.startTransition(() => {
+        fn()
+        setIsTransitioning(false)
+      })
+    }
   }
 
   // Subscribe to location changes