Better javadoc and rename several methods in ApnSetting.

Test: runtest -x frameworks/base/services/tests/servicestests/src/com/android/server/devicepolicy/DevicePolicyManagerTest.java
run cts --module CtsDevicePolicyManagerTestCases --test com.android.cts.devicepolicy.DeviceOwnerTest#testOverrideApn

Bug: 73087996
Change-Id: I5232c92a44ab505946956f81965a205f170aa52b
3 files changed