[SPARK-18137][SQL] Fix RewriteDistinctAggregates UnresolvedException when a UDAF has a foldable TypeCheck

## What changes were proposed in this pull request?

In RewriteDistinctAggregates rewrite funtion,after the UDAF's childs are mapped to AttributeRefference, If the UDAF(such as ApproximatePercentile) has a foldable TypeCheck for the input, It will failed because the AttributeRefference is not foldable,then the UDAF is not resolved, and then nullify on the unresolved object will throw a Exception.

In this PR, only map Unfoldable child to AttributeRefference, this can avoid the UDAF's foldable TypeCheck. and then only Expand Unfoldable child, there is no need to Expand a static value(foldable value).

**Before sql result**

> select percentile_approxy(key,0.99999),count(distinct key),sume(distinc key) from src limit 1
> org.apache.spark.sql.catalyst.analysis.UnresolvedException: Invalid call to dataType on unresolved object, tree: 'percentile_approx(CAST(src.`key` AS DOUBLE), CAST(0.99999BD AS DOUBLE), 10000)
> at org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute.dataType(unresolved.scala:92)
>     at org.apache.spark.sql.catalyst.optimizer.RewriteDistinctAggregates$.org$apache$spark$sql$catalyst$optimizer$RewriteDistinctAggregates$$nullify(RewriteDistinctAggregates.scala:261)

**After sql result**

> select percentile_approxy(key,0.99999),count(distinct key),sume(distinc key) from src limit 1
> [498.0,309,79136]
## How was this patch tested?

Add a test case in HiveUDFSuit.

Author: root <root@iZbp1gsnrlfzjxh82cz80vZ.(none)>

Closes #15668 from windpiger/RewriteDistinctUDAFUnresolveExcep.

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