Change EXTRA_TIME_PREF_24_HOUR_FORMAT from boolean to int

To better represent the possible settings values for the
"use 24 hour format" setting : "12", "24", unset (meaning
"use locale default") the platform is being changed.

The EXTRA_TIME_PREF_24_HOUR_FORMAT for the ACTION_TIME_CHANGED
is now an int, not a boolean. 0 means "12", 1 means "24" and
2 means "use locale default".

Bug: 32761619
Test: Manual test on device and make RunSettingsRoboTests
Change-Id: I9aae6f8d12c4724c829f2812626a6193e510dbf9