Add method to disable "disable" button in installed app UI

OEMs can now force grey out the "disable" button for important apps on
device.

Change-Id: I8ea431b52e50e424be55946f70175db5412e2f4a
Merged-In: Ic075a07ad12592bd60238c7b1c9ab84932c8db3c
Fix: 38250742
Test: make RunSettingsRoboTests