[SPARK-11329] [SQL] Support star expansion for structs.

[nongli]

1. Supporting expanding structs in Projections. i.e.
   "SELECT s.*" where s is a struct type.
   This is fixed by allowing the expand function to handle structs in addition to tables.
2. Supporting expanding * inside aggregate functions of structs.
   "SELECT max(struct(col1, structCol.*))"
   This requires recursively expanding the expressions. In this case, it it the aggregate
   expression "max(...)" and we need to recursively expand its children inputs.

[yhuai]

ok to test

[SparkQA]

Test build #44549 has finished for PR 9343 at commit 54e155e.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * case class UnresolvedStar(target: Option[String]) extends Star with Unevaluable\n

[felixcheung]

'nameas' -> 'name as'?

[SparkQA]

Test build #44555 has finished for PR 9343 at commit df65944.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * class HasSolver(Params):\n * case class UnresolvedStar(target: Option[String]) extends Star with Unevaluable\n

[cloud-fan]

you can make it more dataframe style like testData2.select(struct("a", "b").as("record"))

[SparkQA]

Test build #44704 has finished for PR 9343 at commit be20b33.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * case class UnresolvedStar(target: Option[String]) extends Star with Unevaluable\n

[yhuai]

newChildren => newArgs?

[SparkQA]

Test build #44840 has finished for PR 9343 at commit c55a7d2.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * case class UnresolvedStar(target: Option[Seq[String]]) extends Star with Unevaluable\n

[yhuai]

Seems you want the following?

if (!expandedAttributes.isEmpty) {
  expandedAttributes.zip(input.output).map {
    case (n: NamedExpression, _) => n
    case (e, originalAttribute) =>
      Alias(e, originalAttribute.name)(qualifiers = originalAttribute.qualifiers)
  }
}

[SparkQA]

Test build #44862 has finished for PR 9343 at commit 886acc7.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * case class UnresolvedStar(target: Option[Seq[String]]) extends Star with Unevaluable\n

[yhuai]

nonEmpty?

[yhuai]

Thanks @nongli ! Overall LGTM. I am going to merge it to master. Can you create a follow-up PR to address my comments? Thanks!

[cloud-fan]

please fix the style here. e.g. ).+ instead of ). +, remove the extra { ... }, follow the original indent

[cloud-fan]

We can use exists instead of filter(...).nonEmpty