[SPARK-14863][SQL] Cache TreeNode's hashCode by default

Caching TreeNode's `hashCode` can lead to orders-of-magnitude performance improvement in certain optimizer rules when operating on huge/complex schemas.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #12626 from JoshRosen/cache-treenode-hashcode.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala

@@ -71,7 +71,9 @@ object CurrentOrigin {
   }
 }
 
+// scalastyle:off
 abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
+// scalastyle:on
   self: BaseType =>
 
   val origin: Origin = CurrentOrigin.get
@@ -84,6 +86,9 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] extends Product {
 
   lazy val containsChild: Set[TreeNode[_]] = children.toSet
 
+  private lazy val _hashCode: Int = scala.util.hashing.MurmurHash3.productHash(this)
+  override def hashCode(): Int = _hashCode
+
   /**
    * Faster version of equality which short-circuits when two treeNodes are the same instance.
    * We don't just override Object.equals, as doing so prevents the scala compiler from