[SPARK-4202][SQL] Simple DSL support for Scala UDF

[liancheng]

This feature is based on an offline discussion with @mengxr, hopefully can be useful for the new MLlib pipeline API.

For the following test snippet

case class KeyValue(key: Int, value: String)
val testData = sc.parallelize(1 to 10).map(i => KeyValue(i, i.toString)).toSchemaRDD
def foo(a: Int, b: String) => a.toString + b

the newly introduced DSL enables the following syntax

import org.apache.spark.sql.catalyst.dsl._
testData.select(Star(None), foo.call('key, 'value) as 'result)

which is equivalent to

testData.registerTempTable("testData")
sqlContext.registerFunction("foo", foo)
sql("SELECT *, foo(key, value) AS result FROM testData")

[SparkQA]

Test build #22797 has started for PR 3067 at commit f132818.

• This patch merges cleanly.

[SparkQA]

Test build #22797 has finished for PR 3067 at commit f132818.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • case class ScalaUdfBuilder[T: TypeTag](f: AnyRef)

[AmplabJenkins]

Test PASSed.
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Test PASSed.