Fix setLine1Number Override in SubInfo#getNumber

In Android T, the eventual result of TM#setLine1Number()
was to override the EFmsisdn in case it is incorrect or
not set. That override would propagate to SubscriptionInfo
via an odd-looking hack in SubscriptionController.

This patch restores the behavior of that hack by shadowing
the EFmsisdn as long as the override number is set.

Bug: 325674530
Test: atest TelephonyManagerTest\
      #testSetLine1NumberUpdatesSubscriptionInfo # CTS
Test: # Basic functional test (voice, messaging, data) on Fi
Test: atest SubscriptionManagerServiceTest\
      #testGetNumberWithCarrierNumber
Change-Id: Iabee8fe396de9c3cf29b90145507812b11f4ebb5