Expose Constructor for ModemActivityInfoException

ModemActivityInfoException is a SystemApi but the constructor
is not. There's a longstanding need to expose it for testing.

Bug: 186152174
Test: make update-api && make offline-sdk-docs
Change-Id: I609b4a893e2f4fad54d29e09234da08a45efac78

core/api/system-current.txt

@@ -12312,6 +12312,7 @@ package android.telephony {
   }
 
   public static class TelephonyManager.ModemActivityInfoException extends java.lang.Exception {
+    ctor public TelephonyManager.ModemActivityInfoException(int);
     method public int getErrorCode();
     field public static final int ERROR_INVALID_INFO_RECEIVED = 2; // 0x2
     field public static final int ERROR_MODEM_RESPONSE_ERROR = 3; // 0x3

telephony/java/android/telephony/TelephonyManager.java

@@ -11487,7 +11487,11 @@ public class TelephonyManager {
 
         private final int mErrorCode;
 
-        /** @hide */
+        /**
+         * An exception with ModemActivityInfo specific error codes.
+         *
+         * @param errorCode a ModemActivityInfoError code.
+         */
         public ModemActivityInfoException(@ModemActivityInfoError int errorCode) {
             mErrorCode = errorCode;
         }