[SPARK-32526][SQL]Let sql/catalyst module compile for Scala 2.13

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

@@ -1281,20 +1281,20 @@ class Analyzer(
         }
 
         if (attrMapping.isEmpty) {
-          newPlan -> attrMapping
+          newPlan -> attrMapping.toSeq
         } else {
           assert(!attrMapping.groupBy(_._1.exprId)
             .exists(_._2.map(_._2.exprId).distinct.length > 1),
             "Found duplicate rewrite attributes")
-          val attributeRewrites = AttributeMap(attrMapping)
+          val attributeRewrites = AttributeMap(attrMapping.toSeq)
           // Using attrMapping from the children plans to rewrite their parent node.
           // Note that we shouldn't rewrite a node using attrMapping from its sibling nodes.
           newPlan.transformExpressions {
             case a: Attribute =>
               dedupAttr(a, attributeRewrites)
             case s: SubqueryExpression =>
               s.withNewPlan(dedupOuterReferencesInSubquery(s.plan, attributeRewrites))
-          } -> attrMapping
+          } -> attrMapping.toSeq
         }
       }
     }

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala

@@ -949,7 +949,7 @@ object CombineUnions extends Rule[LogicalPlan] {
           flattened += child
       }
     }
-    union.copy(children = flattened)
+    union.copy(children = flattened.toSeq)
   }
 }