Local and remote isolated storage feature flags.

Moving forward as we start enabling isolated storage in various
dogfood groups, we'll need to maintain separate values for the
feature flag for both "local" and "remote" opinions.  Any strongly
expressed local opinion will always take precidence over any remote
opinion.

Any changes to these feature flags means that we need to invalidate
any PackageManager parsed APKs, since PackageParser changes it's
output depending on the flag state.  Since other feature flags are
likely to need this type of invalidation in the future, define the
PackageManager cache using a SHA-1 hash of a collection of values
that should invalidate the cache.

Bug: 112545973
Test: atest android.os.SystemPropertiesTest
Change-Id: Ifafcdf15e40e694eb4126e06981aeb82df51da33