[Settings] replace isNonTtyOrTtyOnVolteEnabled() and isWfcEnabledByUser() in WFC

1. Code refactor
2. Replace ImsManager#isNonTtyOrTtyOnVolteEnabled() by combination of
   TelecomManager#getCurrentTtyMode() and
   ImsMmTelManager#isTtyOverVolteEnabled()
3. Replace ImsManager#isWfcEnabledByUser() by
ImsMmTelManager#isVoWiFiSettingEnabled()

Bug: 140542283
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=WifiCallingSettingsForSubTest
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=WifiCallingSliceHelperTest
Change-Id: I57c91a095fc4d454d92e8d78e0b647b4f098c6a3