Enable SMS short code patterns to be updated from secure settings.

The premium SMS short code detector loads patterns from an XML resource
by default (frameworks/base/core/res/res/xml/sms_short_codes.xml).
Add support for updated patterns to be loaded on a per-country basis
from a secure setting named "sms_short_codes_" + the country code.
Updated patterns can be pushed to Google devices via Gservices.

Bug: 5513975
Change-Id: Ibfc0be4f12227ba45c28396ec7cdbc307442af81