Add route info migration guide (#8467)

Migration guide for flutter/flutter#119968

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---------

Co-authored-by: Loïc Sharma <737941+loic-sharma@users.noreply.github.com>

src/release/breaking-changes/index.md

@@ -21,10 +21,12 @@ release, and listed in alphabetical order:
 * [Deprecated API removed after v3.7][]
 * [Removed `ignoringSemantics`][]
 * [The window singleton is deprecated][]
+* [Migration guide for `RouteInformation.location`][]
 
 [Deprecated API removed after v3.7]: {{site.url}}/release/breaking-changes/3-7-deprecations
 [Removed `ignoringSemantics`]: {{site.url}}/release/breaking-changes/ignoringsemantics-migration
 [The window singleton is deprecated]: {{site.url}}/release/breaking-changes/window-singleton
+[Migration guide for `RouteInformation.location`]: {{site.url}}/release/breaking-changes/route-information-uri
 
 ### Released in Flutter 3.7
 

src/release/breaking-changes/route-information-uri.md

@@ -0,0 +1,97 @@
+---
+title: Migration guide for `RouteInformation.location`
+description: Deprecation of `RouteInformation.location` and its related APIs
+---
+
+## Summary
+
+`RouteInformation.location` and related APIs were deprecated in the favor of `RouteInformation.uri`.
+
+## Context
+
+The [`RouteInformation`][] needs the authority information to handle mobile deeplinks from different web domains. The `uri` field was added to `RouteInformation` that captures the entire deeplink information and route-related parameters were converted to the full [`Uri`][] format. This led to deprecation of incompatible APIs.
+
+## Description of change
+
+* The `RouteInformation.location` was replaced by `RouteInformation.uri`.
+* The `WidgetBindingObserver.didPushRoute` was deprecated.
+* The `location` parameter of `SystemNavigator.routeInformationUpdated` was replaced by the newly added `uri` parameter.
+
+## Migration guide
+
+Code before migration:
+
+```dart
+const RouteInformation myRoute = RouteInformation(location: '/myroute');
+```
+
+Code after migration:
+
+```dart
+final RouteInformation myRoute = RouteInformation(uri: Uri.parse('/myroute'));
+```
+
+Code before migration:
+
+```dart
+final String myPath = myRoute.location;
+```
+
+Code after migration:
+
+```dart
+final String myPath = myRoute.uri.path;
+```
+
+Code before migration:
+
+```dart
+class MyObserverState extends State<MyWidget> with WidgetsBindingObserver {
+  @override
+  Future<bool> didPushRoute(String route) => _handleRoute(route);
+}
+```
+
+Code after migration:
+
+```dart
+class MyObserverState extends State<MyWidget> with WidgetsBindingObserver {
+  @override
+  Future<bool> didPushRouteInformation(RouteInformation routeInformation) => _handleRoute(
+    Uri.decodeComponent(
+      Uri(
+        path: uri.path.isEmpty ? '/' : uri.path,
+        queryParameters: uri.queryParametersAll.isEmpty ? null : uri.queryParametersAll,
+        fragment: uri.fragment.isEmpty ? null : uri.fragment,
+      ).toString(),
+    )
+  );
+}
+```
+
+Code before migration:
+
+```dart
+SystemNavigator.routeInformationUpdated(location: '/myLocation');
+```
+
+Code after migration:
+
+```dart
+SystemNavigator.routeInformationUpdated(uri: Uri.parse('/myLocation'));
+```
+
+## Timeline
+
+Landed in version: 3.9.0-18.0.pre-93-gf9095ef022<br>
+In stable release: TBD
+
+## References
+
+Relevant PRs:
+
+* [PR 119968][]: Implement url support for RouteInformation and didPushRouteInformation.
+
+[PR 119968]: {{site.repo.flutter}}/pull/119968
+[`RouteInformation`]: {{site.api}}/flutter/widgets/RouteInformation-class.html
+[`Uri`]: {{site.api}}/flutter/dart-core/Uri-class.html