Explicitly use overridden or non-overridden roaming state.

- Deliver the overridden boolean isRoaming to TelephonyDisplayInfo.
- Use the non-overridden registration state from network instead of
  the initial registration state.

Bug: 260017781
Test: atest DisplayInfoControllerTest
Merged-In: I1e54aafcca9e720d9a9fe718553e6f13cef1922b
Change-Id: I1e54aafcca9e720d9a9fe718553e6f13cef1922b