Default SessionCatalog should support UDFs

SessionCatalog calls registerFunction to add a function to function registry. However, makeFunctionExpression supports only UserDefinedAggregateFunction.

We should make makeFunctionExpression support UserDefinedFunction, as it's one of functions type.

Currently we can use persistent functions only with Hive metastore, but "create function" command works also with default SessionCatalog. It sometimes cause user confusion, like in https://stackoverflow.com/questions/52164488/spark-hive-udf-no-handler-for-udaf-analysis-exception/52170519