## Description

Similar to #119877, but with more cases that I could find in `packages/flutter`. 

Although there is already a [proposal](https://github.com/dart-lang/linter/issues/4102), it is uncertain how long it will take to be implemented.

![[image-20200711205959042](https://user-images.githubusercontent.com/72788825/216486897-b56453d2-b309-47ea-885b-b0ec6ed1b648.png)](https://user-images.githubusercontent.com/72788825/216486897-b56453d2-b309-47ea-885b-b0ec6ed1b648.png)

### Description
- Fixes https://github.com/flutter/flutter/issues/134205.

### Tests
- Removes ignoring the `_RestorableRouteInformation` leak from `cupertino/app_test.dart`;
- Removes ignoring the `_RestorableRouteInformation` leak from `material/app_test.dart`;
- Removes ignoring the `_RestorableRouteInformation` leak from `widgets/app_test.dart`;
- Removes ignoring the `_RestorableRouteInformation` leak from `widgets/route_notification_messages_test.dart`;
- Removes ignoring the `_RestorableRouteInformation` leak from `widgets/router_restoration_test.dart`;
- Updates `widgets/router_test.dart` to use `testWidgetsWithLeakTracking`.

Reverts flutter/flutter#134953

Several failures on CI

Related https://github.com/flutter/flutter/issues/100624

The goal is to make sure the engine can send a location string in either the existing format or a complete uri string to the framework, and the framework will still work as usual.

* Use `curly_braces_in_flow_control_structures` for `widgets`

* fix comments

* fix comments

This reverts commit 35ad43f2.

This reverts commit c26ed03c.

* Migrate to ChannelBuffers.push

* Move TestDefaultBinaryMessenger to its own file

* Apply deprecations and fix usages

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag