base: Phone ringtone setting for Multi SIM device [1/3]

Add below changes to handle default phone ringtone for slot2.
1. Add Settings.System.RINGTONE2 as the key in SettingsProvider to
save ringtone for slot2.
2. Support "ro.config.ringtone" for Multi SIM device.
3. Adapt ringtone for slot2 in current ringtone related APIs.

Bug: 118735436
Test: Manual
Change-Id: I9c6ccff938122332d222853d469ad9a623c7d193

Fixup after A14_r17

Change-Id: I65791ce1c17d99d60966c9405c12d4b2a309787f
6 files changed