[SPARK-34004][SQL] Change FrameLessOffsetWindowFunction as sealed abstract class

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala

@@ -2150,9 +2150,6 @@ class Analyzer(override val catalogManager: CatalogManager)
                         lead.copy(ignoreNulls = ignoreNulls)
                       case lag: Lag =>
                         lag.copy(ignoreNulls = ignoreNulls)
-                      case _ =>
-                        throw QueryCompilationErrors.functionWithUnsupportedSyntaxError(
-                          owf.prettyName, "IGNORE NULLS")
                     }
                   } else {
                     owf

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala

@@ -369,7 +369,7 @@ trait OffsetWindowFunction extends WindowFunction {
  * within the partition. For instance: a FrameLessOffsetWindowFunction for value x with offset -2,
  * will get the value of x 2 rows back from the current row in the partition.
  */
-abstract class FrameLessOffsetWindowFunction
+sealed abstract class FrameLessOffsetWindowFunction
   extends OffsetWindowFunction with Unevaluable with ImplicitCastInputTypes {
 
   override def children: Seq[Expression] = Seq(input, offset, default)