Add isEmergencyApn

DcTracker uses this to make sure emergency APNs are not set for initial
attach. This is used instead of canHandleType because it doesn't depend
on the APN being enabled.

Bug: 144932430
Test: manual
Change-Id: I642c7d2171adb862751a5022a9b613ab58b22bf8

telephony/java/android/telephony/data/ApnSetting.java

@@ -1055,6 +1055,11 @@ public class ApnSetting implements Parcelable {
         return (mApnTypeBitmask & type) == type;
     }
 
+    /** @hide */
+    public boolean isEmergencyApn() {
+        return hasApnType(TYPE_EMERGENCY);
+    }
+
     /** @hide */
     public boolean canHandleType(@ApnType int type) {
         if (!mCarrierEnabled) {