[Settings Telephony] Carrier name API replacement

Replacing TelephonyManager.getNetworkOperatorName() by
Obtaining carrier name from SubscriptionInfo.getCarrierName().

TelephonyManager.getNetworkOperatorName() only be used when there's no
SubscriptionInfo can be found.

Bug: b/140443508
Test: Manual testing
  atest MobileNetworkUtilsTest
  atest OpenNetworkSelectPagePreferenceControllerTest

Change-Id: I7a86395c86d31fe2ba54c04ac16b1a0ebfc843f3