The `generate_gradle_lockfiles` script currently writes the top level `build.gradle` file and the `settings.gradle` file, and is the easiest way to batch update these files to, for example, increase the AGP version used in integration tests and examples across the framework repo.
This PR makes it also write the gradle version, so that we can do batch upgrades of our gradle version with it as well.
This PR updates almost* all Gradle buildscripts in the Flutter repo the `example` and `dev` (in particular, in `dev/integration_tests` and in `dev/benchmarks`) directories to apply Flutter's Gradle plugins using the declarative `plugins {}` block.
*almost, because:
- add-to-app (aka hybrid) apps are not migrated (related https://github.com/flutter/flutter/issues/138756)
- apps that purposefully use build files to ensure backward compatibility (e.g. [`gradle_deprecated_settings`](https://github.com/flutter/flutter/tree/3.16.0/dev/integration_tests/gradle_deprecated_settings))
Upgrades agp versions and lockfiles for `dev/`. Also changes the lockfile generation script to represent the newer form of the `settings.gradle` template, and therefore also propagates these changes.
~~Potentially related to https://github.com/flutter/flutter/issues/134419~~, but worth doing anyways. (not actually related)
The `generate_gradle_lockfiles.dart` script was generating the gradle wrapper by building a flavor that didn't exist. In the time since the script was written, the `--config-only` flag was created and should be used instead.
Context https://github.com/flutter/flutter/pull/132406#discussion_r1300352602
