### What changes were proposed in this pull request?
This PR proposes to use `ExpressionEncoder` for the return type of ScalaUDF to convert to the catalyst type, instead of using `CatalystTypeConverters`.
Note, this change only takes effect for typed Scala UDF since its the only case where we know the type tag of the raw type.
### Why are the changes needed?
Users now could register a UDF with `Instant`/`LocalDate` as return types even with `spark.sql.datetime.java8API.enabled=false`. However, the UDF can not really be used.
For example, if we try:
```scala
scala> sql("set spark.sql.datetime.java8API.enabled=false")
scala> spark.udf.register("buildDate", udf{ d: String => java.time.LocalDate.parse(d) })
scala> Seq("2020-07-02").toDF("d").selectExpr("CAST(buildDate(d) AS STRING)").show
```
Then, we will hit the error:
```scala
java.lang.ClassCastException: java.time.LocalDate cannot be cast to java.sql.Date
at org.apache.spark.sql.catalyst.CatalystTypeConverters$DateConverter$.toCatalystImpl(CatalystTypeConverters.scala:304)
at org.apache.spark.sql.catalyst.CatalystTypeConverters$CatalystTypeConverter.toCatalyst(CatalystTypeConverters.scala:107)
at org.apache.spark.sql.catalyst.CatalystTypeConverters$.$anonfun$createToCatalystConverter$2(CatalystTypeConverters.scala:425)
at org.apache.spark.sql.catalyst.expressions.ScalaUDF.eval(ScalaUDF.scala:1169)
...
```
as it actually requires enabling `spark.sql.datetime.java8API.enabled` when using the UDF. And I think this could make users get confused.
This happens because when registering the UDF, Spark actually uses `ExpressionEncoder` to ser/deser types. However, when using UDF, Spark uses `CatalystTypeConverters`, which is under control of `spark.sql.datetime.java8API.enabled`, to ser/deser types. Therefore, Spark would fail to convert the Java8 date time types.
If we could also use `ExpressionEncoder` to ser/deser types for the return type, similar to what we do for the input parameter types, then, UDF could support Instant/LocalDate, event other combined complex types as well.
### Does this PR introduce _any_ user-facing change?
Yes. Before this PR, if users run the demo above, they would hit the error. After this PR, the demo will run successfully.
### How was this patch tested?
Updated 2 tests and added a new one for combined types of `Instant` and `LocalDate`.
Closes#28979 from Ngone51/udf-return-encoder.
Authored-by: yi.wu <yi.wu@databricks.com>
Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>
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