SystemUI: Display RAT icon when data is off

Introduce customization and implementation to display RAT icon in status
bar even when data is off. Since some carriers require, this feature is
necessary.

Test: Test with simulated RIL
Bug: 28805511
Change-Id: I0428ba1749bdb884d210f1ff02cdf86b376a0ca8
diff --git a/telephony/java/android/telephony/CarrierConfigManager.java b/telephony/java/android/telephony/CarrierConfigManager.java
index 1d08111..e0bd05d 100644
--- a/telephony/java/android/telephony/CarrierConfigManager.java
+++ b/telephony/java/android/telephony/CarrierConfigManager.java
@@ -947,6 +947,12 @@
     public static final String KEY_STK_DISABLE_LAUNCH_BROWSER_BOOL =
             "stk_disable_launch_browser_bool";
 
+    /**
+     * Boolean indicating if show data RAT icon on status bar even when data is disabled
+     * @hide
+     */
+    public static final String KEY_ALWAYS_SHOW_DATA_RAT_ICON_BOOL =
+            "always_show_data_rat_icon_bool";
 
     // These variables are used by the MMS service and exposed through another API, {@link
     // SmsManager}. The variable names and string values are copied from there.
@@ -1925,6 +1931,7 @@
         sDefaults.putStringArray(KEY_FEATURE_ACCESS_CODES_STRING_ARRAY, null);
         sDefaults.putBoolean(KEY_IDENTIFY_HIGH_DEFINITION_CALLS_IN_CALL_LOG_BOOL, false);
         sDefaults.putBoolean(KEY_SPN_DISPLAY_RULE_USE_ROAMING_FROM_SERVICE_STATE_BOOL, false);
+        sDefaults.putBoolean(KEY_ALWAYS_SHOW_DATA_RAT_ICON_BOOL, false);
     }
 
     /**