Convert Skottie build instructions to build an Android Library (AAR) instead of app (APK)

Change-Id: Ib12364792523ac896c74ce2cd563173dd6081e78
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/296417
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Jorge Betancourt <jmbetancourt@google.com>
13 files changed