nn: git-merge upstream/master into ToT

This should allow us to bring the two trees into sync, which will make
future merges cleaner and retain better commit history from upstream
without needing to cherry-pick individual commits.

BUG=b:157855577
TEST=FEATURES=test emerge-betty aosp-frameworks-ml-nn

Change-Id: I5ff36d8a49d584db0e656c24cf60c67dcefa8de2