[Settings] Code refactor for Wifi calling IMS API

Replacing logics of
ImsManager#isWfcEnabledByPlatform() &
MobileNetworkUtils#isWfcProvisionedOnDevice()
into WifiCallingQueryImsState#isWifiCallingProvisioned().

Bug: 140542283
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=WifiCallingSliceHelperTest
Merged-In: I68462368669b81e10d09bbb93e74e23ea9a1f446
Change-Id: I26d616f082a4dd3f2cb14defc5f68218f668ad48