Update FeatureSplit sample

This updates the FeatureSplit test sample to reflect the current
way of doing correct feature splits.

This is not final, as aapt2 will be gaining some improvements to
make access of private resources across feature splits valid by default.

Bug: 65096694
Test: manual
Change-Id: I4524dc161d46c5479b5abe340eb93844078ed316
7 files changed