[SB Refactor] Update the wifi network flow to use stateIn so that new

subscribers will receive the current value.

See linked bug for more details.

Fixes: 244173280
Test: manual: turn off wifi then look at icon in QS and lockscreen.
Verify QS and lockscreen show an updated wifi icon. (See video in bug)
Test: WifiRepositoryImplTest

Change-Id: I22910a15eb2e9755723e6e55c60357389273f8cf