Adding "wifi only" option for wifi calling.

- Added "wifi-only" option to the list of wifi calling modes.
- Added code in settings initialization to check whether the carrier
supports including the wifi-only option.  If it does not, changes the
entries/values to a ser which does not include the wifi-only option.

Bug: 27858149
Change-Id: Ib02a97afcf6f2722c28b7a4d9c241774944c52d0

res/values/strings.xml

@@ -1965,10 +1965,20 @@
     <string-array name="wifi_calling_mode_choices">
         <item>Wi-Fi preferred</item>
         <item>Cellular preferred</item>
+        <item>Wi-Fi only</item>
     </string-array>
     <string-array name="wifi_calling_mode_values">
         <item>"2"</item>
         <item>"1"</item>
+        <item>"0"</item>
+    </string-array>
+    <string-array name="wifi_calling_mode_choices_without_wifi_only">
+        <item>Wi-Fi preferred</item>
+        <item>Cellular preferred</item>
+    </string-array>
+    <string-array name="wifi_calling_mode_values_without_wifi_only">
+        <item>"2"</item>
+        <item>"1"</item>
     </string-array>
     <!-- Wi-Fi Calling settings. Text displayed when Wi-Fi Calling is off -->
     <string name="wifi_calling_off_explanation">When Wi-Fi calling is on, your phone can route calls via Wi-Fi networks or your carrier\u2019s network, depending on your preference and which signal is stronger. Before turning on this feature, check with your carrier regarding fees and other details.</string>