Support secondary locales

Add support for tracking a secondary locale in addition to the current
primary locale for CP2. Switch to using parseable ICU language tag
(eg, "en-US") for locale tag written to DB. Secondary locale is set to
previous locale on locale change and persisted in CP2 DB and prefs.

Bug:8715226
Change-Id: Ia68397fd9118d89f3a45ac54f991f86bad42870e
8 files changed