Add androidx.annotation_annotation dependency.

stats-log-api-gen adds missing @RequiresApi annotations to the generated
StatsLog.write() calls. The library pulling in the changes needs to
depend on androidx.annotation_annotation which provides @RequiresApi
annotation.

Bug: 319044160
Test: m docsui-statsd
Change-Id: I47caef3470882478fca48fc1cca9fad78763818b