Compose Message "To" field allows adding sequence of characters as contact

When we select this option, this sequence of characters (which is neither a
valid email address nor a phone number), gets stored in contact with type MOBILE.

Fix: In function canAddToContacts, adding a check to validate whether the contact
to be added is a valid email address or phone number. If not, user will not be shown
with the option "Add to Contacts".

core/java/android/provider/Telephony.java

@@ -1263,6 +1263,21 @@ public final class Telephony {
             return match.matches();
         }
 
+        /**
+         * Returns true if the number is a Phone number
+         *
+         * @param number the input number to be tested
+         * @return true if number is a Phone number
+         */
+        public static boolean isPhoneNumber(String number) {
+            if (TextUtils.isEmpty(number)) {
+                return false;
+            }
+
+            Matcher match = Regex.PHONE_PATTERN.matcher(number);
+            return match.matches();
+        }
+
         /**
          * Contains all MMS messages in the MMS app's inbox.
          */