Set previous_api correctly for java_sdk_library

Metalava used this attribute to potentially re-write some nullness
annotations from @Nullable to @RecentlyNonNull, and not doing so can
cause problems when compiling kotlin.

Bug: 176092452
Test: m art.module.public.api.stubs && \
      rm -rf /tmp/lib && \
      unzip -qd /tmp/lib art.module.public.api.stubs.jar && \
      javap -v /tmp/lib/java/util/concurrent/ConcurrentHashMap.class | \
      grep Recently
Change-Id: I9012798f27e39d9a53dbcf0976548f6cec2d3150