[VL] Map unbase64 to a Velox function name

### Description

The`from_base64` function provided by perstosql, it's the same functionality as `unbase64`, and I think we can map the sparksql function `unbase64` to `from_base64`.

The Spark functions doc link is : https://spark.apache.org/docs/latest/api/sql/index.html#unbase64
The Presto functions doc link is : https://prestodb.github.io/docs/current/functions/binary.html