[DataFrame][minor] support column in field accessor

Minor improvement, now we can use `Column` as extraction expression.

Author: Wenchen Fan <cloud0fan@outlook.com>

Closes #6080 from cloud-fan/tmp and squashes the following commits:

0fdefb7 [Wenchen Fan] support column in field accessor

sql/core/src/main/scala/org/apache/spark/sql/Column.scala

@@ -78,7 +78,7 @@ class Column(protected[sql] val expr: Expression) extends Logging {
    *
    * @group expr_ops
    */
-  def apply(field: Any): Column = UnresolvedExtractValue(expr, Literal(field))
+  def apply(extraction: Any): Column = UnresolvedExtractValue(expr, lit(extraction).expr)
 
   /**
    * Unary minus, i.e. negate the expression.

sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala

@@ -456,6 +456,7 @@ class DataFrameSuite extends QueryTest {
     assert(complexData.filter(complexData("a")(0) === 2).count() == 1)
     assert(complexData.filter(complexData("m")("1") === 1).count() == 1)
     assert(complexData.filter(complexData("s")("key") === 1).count() == 1)
+    assert(complexData.filter(complexData("m")(complexData("s")("value")) === 1).count() == 1)
   }
 
   test("SPARK-7324 dropDuplicates") {