Make some device info related slices public.

Only PreferenceControllers with isPublicSlice() set to true are exposed
to other apps. Others will be Settings only.

Bug: 141088937
Test: robotests
Change-Id: Id38fd0203a4efc812e30990491786b4d8aff8902

src/com/android/settings/deviceinfo/PhoneNumberPreferenceController.java

@@ -95,6 +95,11 @@ public class PhoneNumberPreferenceController extends BasePreferenceController {
         return true;
     }
 
+    @Override
+    public boolean isPublicSlice() {
+        return true;
+    }
+
     @Override
     public boolean isCopyableSlice() {
         return true;