Deferring applicationId retrieval to when the publishApkTask runs

[ZacSweers]

Right now, the applicationId is captured at configuration and persisted throughout the PlayPublishTask's lifetime, even though a build might dynamically change the applicationId after that. Retrieving the APK file would run into the same issue if the developer set custom APK names, but it doesn't run until the PlayPublishApkTask runs, and thus retrieves the correct final name after the app has been assembled. My proposal is to do the same with applicationId. I think it would be an easy change, since the variant instance is held in the PlayPublishApkTask.

In PlayPublishApkTask, instead of using the saved applicationId field, we can simply call variant.applicationId. I think this should work, though it might have to be variant.mergedFlavor.applicationId (I'm not entirely sure if they can ever be different).

If you're open to it, I'd be happy to send a pull request your way.

[bhurling]

Sounds good.

[ZacSweers]

Great, I'll get started on it tomorrow!