Bump almost all tests to AGP 8.1 and Gradle 8.3
Flutter gallery is excluded, because it uses discontinued plugins that in turn use old Gradle versions, and that prevents upgrading. Will take some extra work to figure out what to do there.
Should bump templates next
Entire PR generated with the lockfile generation script, except for:
1. changes within `dev/integration_tests/gradle_deprecated_settings/android/`, which must be done manually (and exclusion of the gallery for reason mentioned above).
2. Changes to many `AndroidManifest.xml` files to remove the `package` attribute and instead set that same value in the `build.gradle`, in the `namespace` attribute of the `android` closure (corresponds to an AGP behavior change, see https://d.android.com/r/tools/upgrade-assistant/set-namespace).
3. Removes the use of the `battery` plugin in `android_embedding_v2_smoke_test` because the plugin is discontinued, unused, and blocks upgrading the AGP version for that app because the discontinued plugin itself uses a very old AGP version.
The script currently overwrites existing `settings.gradle`, `build.gradle`, and `gradle-wrapper.properties` files in the directories it processes. This mode makes it not do that, and just generate the lockfiles themselves.
Related to https://github.com/flutter/flutter/pull/145564#r1371888460
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
