Update AlarmManager javadoc for S Beta 3

Sample partial output: https://screenshot.googleplex.com/4wey3a3y3jsoGcP

Bug: 190625528
Test: build
Test: m offline-sdk-docs && \
  cd /android/sc-dev/out/target/common/docs/offline-sdk/ && \
  python3 -m http.server 8000 && \
  google-chrome http://localhost:8000/reference/android/app/AlarmManager.html#setExactAndAllowWhileIdle(int,%20long,%20android.app.PendingIntent)
Change-Id: Ie106b03a1c20fa62b0023f82d2c3997b4e425d95