watchlist: Optimize hash code computation for APK.

ARC team require no divergence with main branch. That is why
this CL is upstreamed and disabled by default for Android and
activated in ARC using config flag.

This service has following features:
   * Aggregated report once per day.
   * Report network operations.
Each above has associated uid that is computed per apks for user id. For
agregated report this means involving most of apks. As as result each
apk is read. Particular this means reading most apks from the system
image during the initial boot and once per day next. In ARC this means
access to squashFS method which is heavy operation. This implements
persistent cache for apk hashes.

Notes: This cherry pick also includes ag/14268703 and ag/19700959.

Test: Locally, no problem found.
      tast.AuthPerf server reports 1+ second improvement in case caches
      are pregenerated However effect of this last longer. Usually
      agregated report takes more time than test run.
      Traced access to squashFS for decompression operations during the
      full initial but. After includes pre-generated cache.
         Before: Compressed 329MB -> Decompressed 804MB in 35 sec.
         After:  Compressed 266MB -> Decompressed 676MB in 22 sec.
Bug: 148229706

Change-Id: I30fbfcb43ff617e57773099e59d50adc1dbebe2c
(cherry picked from commit 2f2dac8c0c7801f4384c3e36a1e8b8bc24471fc7)
(cherry picked from commit ffcad8d2b183708519dddca23a1e21142f4aad20)
(cherry picked from commit 9004131f17d8cbdcea0ea1f8711af1067d4fb804)