[Provider Model] Implement the carrner network selection

- Add primaryAction for connecting carrier network

- User toggles carrier network On/Off
  - Calls MergedCarrierEntry#setEnabled(true/false)

- User taps on carrier network
  - Calls MergedCarrierEntry#connect()

Bug: 175761096
Test:
- Manual Test
- atest ProviderModelSliceTest
- atest ProviderModelSliceHelperTest
- make RunSettingsRoboTests ROBOTEST_FILTER=WifiScanWorkerTest

Change-Id: I07cb6c142a2f4e9cbdbab1f77afdc367728b4e3f