Special handling of JSON type for MySQL Connector/J 5.x

MySQL JDBC driver `mysql-connector-java-5.1.49.jar` converts JSON type into Types.CHAR with a precision of Int.Max.
When receiving CHAR with Int.Max precision, Spark executor will throw an error of `java.lang.OutOfMemoryError: Requested array size exceeds VM limit `.

For mysql-connector-java-5.1.49.jar json sqlType is Char and precision is Int.Max.
For mysql-connector-java-8.0.16.jar json sqlType is LONGVARCHAR and precision is Int.Max.

Spark use mysql-connector-java-8.0.16.jar is right.

private def getCatalystType(
      sqlType: Int,
      typeName: String,
      precision: Int,
      scale: Int,
      signed: Boolean,
      isTimestampNTZ: Boolean): DataType = sqlType match{     
    ...     
    case java.sql.Types.LONGNVARCHAR => StringType    
    ...   
}

If compatibility with 5.1.49 is not required, the current code is sufficient.