Autobuild ignores default build variant setting for Android projects

CodeQL autobuild apparently always tries to build the alphabetically earliest build variant for an Android project, ignoring alternate default build variant settings specified in `build.gradle`:

- https://issuetracker.google.com/issues/36988145
- https://stackoverflow.com/questions/52072162/how-to-change-android-studios-default-build-flavor

For example, my project [SMS Import / Export](https://github.com/tmo1/sms-ie) has four build variants, and the default is set to `standardDebug`. Android Studio respects this, but CodeQL autobuild still tries to build `legacyDebug`.

Start by tracing CodeQL's Android autobuild handling and how it determines the build variant from the project's build.gradle. Reproduce the issue with the linked SMS Import / Export project, which defines standardDebug as its default while autobuild selects legacyDebug. Done means autobuild respects the configured default variant.

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