Fix warning in flutter created project ("package attribute is deprecated" in AndroidManifest)

[bartekpacia]

This PR resolves #123302

Learn more:

• Android Developers | Configure the app module

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[goderbauer]

@reidbaker Can someone with Android expertise take a look at this, please?

[reidbaker]

Does this also fix #123636 (which I filed before seeing this PR)

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auto label is removed for flutter/flutter, pr: 123426, due to This PR has not met approval requirements for merging. You have project association CONTRIBUTOR and need 1 more review(s) in order to merge this PR.

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[auto-submit]

auto label is removed for flutter/flutter, pr: 123426, due to Validations Fail.

[gnprice]

LGTM, thanks!

It would be good to make a migration for this, too, so that Flutter developers don't get this warning in existing apps. But that would have to come after upgrading Gradle, #122376. (Or else be conditional on the Gradle version, but seems simplest to just sequence it after upgrading Gradle.)

edit: Oh, more to the point: it would have to come after upgrading AGP (to at least 7.3, where this "namespace" feature was introduced). But that in turn will require upgrading Gradle.

[gnprice]

Does this also fix #123636 (which I filed before seeing this PR)

No — this PR doesn't affect what AGP version (or Gradle version) is used. It just migrates off of using a deprecated bit of the API of AGP, to a new API that was introduced in a recent AGP.