The current implementation of statistics of UnaryNode does not considering output (for example, Project may product much less columns than it's child), we should considering it to have a better guess.

We usually only join with few columns from a parquet table, the size of projected plan could be much smaller than the original parquet files. Having a better guess of size help we choose between broadcast join or sort merge join.

After this PR, I saw a few queries choose broadcast join other than sort merge join without turning spark.sql.autoBroadcastJoinThreshold for every query, ended up with about 6-8X improvements on end-to-end time.

We use `defaultSize` of DataType to estimate the size of a column, currently For DecimalType/StringType/BinaryType and UDT, we are over-estimate too much (4096 Bytes), so this PR change them to some more reasonable values. Here are the new defaultSize for them:

DecimalType:  8 or 16 bytes, based on the precision
StringType:  20 bytes
BinaryType: 100 bytes
UDF: default size of SQL type

These numbers are not perfect (hard to have a perfect number for them), but should be better than 4096.

Author: Davies Liu <davies@databricks.com>

Closes #11210 from davies/statics.