We store the initial subId and check if it has changed so that we always
have the updated subscription info in fillList().
Fixes: 111731641
Test: manually verify that swapping the SIM loads new APNs
Change-Id: I3475915f2c380fb67b2e56436423d491e489d91e
Merged-In: I29492ef016c8ca9836ecf28c787e441629cfecb0
This is a clean up CL, move the apn settings related class from settings'
root to network's directory.
Bug: 77339683
Test: make ROBOTEST_FILTER=ApnEditorTest -j40 RunSettingsRoboTests
Change-Id: I751a6c2a27c9a1e08d7308407d75ccb355f295aa