[go_router] Fix Android Cold Start deep link with empty path losing scheme and authority. (#9868)

### Description
Fixes an issue where deep links with empty paths (e.g., `https://example.com`) lose their scheme and authority information during Android Cold Start.

This PR fixes flutter/flutter#174249

Detailed reproduction steps, environment information, and code sample are provided in the linked issue.

### Problem
On Android Cold Start, if the initial deep link has no path (`https://example.com`),  
`_effectiveInitialLocation` incorrectly creates a new `Uri` with only `/?` instead of preserving scheme and authority.  
This results in the router receiving a relative path instead of the full deep link URL.

### Solution
Use `Uri.replace(path: '/')` instead of creating a new `Uri`, so that the original scheme and authority are preserved.

## Pre-Review Checklist

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Author: nozomemein

packages/go_router/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 16.2.4
+
+- Fix Android Cold Start deep link with empty path losing scheme and authority.
+
 ## 16.2.3
 
 - Fixes an issue where iOS back gesture pops entire ShellRoute instead of the active sub-route.

packages/go_router/lib/src/router.dart

@@ -574,12 +574,7 @@ class GoRouter implements RouterConfig<RouteMatchList> {
       WidgetsBinding.instance.platformDispatcher.defaultRouteName,
     );
     if (platformDefaultUri.hasEmptyPath) {
-      // TODO(chunhtai): Clean up this once `RouteInformation.uri` is available
-      // in packages repo.
-      platformDefaultUri = Uri(
-        path: '/',
-        queryParameters: platformDefaultUri.queryParameters,
-      );
+      platformDefaultUri = platformDefaultUri.replace(path: '/');
     }
     final String platformDefault = platformDefaultUri.toString();
     if (initialLocation == null) {

packages/go_router/pubspec.yaml

@@ -1,7 +1,7 @@
 name: go_router
 description: A declarative router for Flutter based on Navigation 2 supporting
   deep linking, data-driven routes and more
-version: 16.2.3
+version: 16.2.4
 repository: https://github.com/flutter/packages/tree/main/packages/go_router
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+go_router%22
 

packages/go_router/test/go_router_test.dart

@@ -3371,7 +3371,7 @@ void main() {
         final GoRouter router = await createRouter(routes, tester);
         expect(
           router.routeInformationProvider.value.uri.toString(),
-          '/?param=1',
+          'https://domain.com/?param=1',
         );
         TestWidgetsFlutterBinding.instance.platformDispatcher
             .clearDefaultRouteNameTestValue();