[Settings] Create a proxy for SubscriptionManager

There're many access from Settings app to SubscriptionManager.
Lots of them are checking for similar information.
Create a proxy can reduce the number of inter-process access from
Settings app to SubscriptionManager, and improve Settings app's
UI performance.

Bug: 141833767
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=GlobalSettingsChangeListenerTest
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=ActiveSubsciptionsListenerTest
Change-Id: I3591c478045500a97245955767a7ddd5d361da77