[SPARK-26352][SQL][FOLLOWUP-2.4] Fix missing sameOutput in branch-2.4

## What changes were proposed in this pull request?

After #23303 was merged to branch-2.3/2.4, the builds on those branches were broken due to missing a `LogicalPlan.sameOutput` function which came from #22713 only available on master.

This PR is to follow-up with the broken 2.3/2.4 branches and make a copy of the new `LogicalPlan.sameOutput` into `ReorderJoin` to make it locally available.

## How was this patch tested?

Fix the build of 2.3/2.4.

Closes #23330 from rednaxelafx/clean-build-2.4.

Authored-by: Kris Mok <rednaxelafx@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

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

@@ -100,14 +100,29 @@ object ReorderJoin extends Rule[LogicalPlan] with PredicateHelper {
         createOrderedJoin(input, conditions)
       }
 
-      if (p.sameOutput(reordered)) {
+      if (sameOutput(p, reordered)) {
         reordered
       } else {
         // Reordering the joins have changed the order of the columns.
         // Inject a projection to make sure we restore to the expected ordering.
         Project(p.output, reordered)
       }
   }
+
+  /**
+   * Returns true iff output of both plans are semantically the same, ie.:
+   *  - they contain the same number of `Attribute`s;
+   *  - references are the same;
+   *  - the order is equal too.
+   * NOTE: this is copied over from SPARK-25691 from master.
+   */
+  def sameOutput(plan1: LogicalPlan, plan2: LogicalPlan): Boolean = {
+    val output1 = plan1.output
+    val output2 = plan2.output
+    output1.length == output2.length && output1.zip(output2).forall {
+      case (a1, a2) => a1.semanticEquals(a2)
+    }
+  }
 }
 
 /**

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinReorderSuite.scala

@@ -291,13 +291,28 @@ class JoinReorderSuite extends PlanTest with StatsEstimationTestBase {
     val optimized = Optimize.execute(analyzed)
     val expected = groundTruthBestPlan.analyze
 
-    assert(analyzed.sameOutput(expected)) // if this fails, the expected plan itself is incorrect
-    assert(analyzed.sameOutput(optimized))
+    assert(sameOutput(analyzed, expected)) // if this fails, the expected plan itself is incorrect
+    assert(sameOutput(analyzed, optimized))
 
     compareJoinOrder(optimized, expected)
   }
 
   private def outputsOf(plans: LogicalPlan*): Seq[Attribute] = {
     plans.map(_.output).reduce(_ ++ _)
   }
+
+  /**
+   * Returns true iff output of both plans are semantically the same, ie.:
+   *  - they contain the same number of `Attribute`s;
+   *  - references are the same;
+   *  - the order is equal too.
+   * NOTE: this is copied over from SPARK-25691 from master.
+   */
+  def sameOutput(plan1: LogicalPlan, plan2: LogicalPlan): Boolean = {
+    val output1 = plan1.output
+    val output2 = plan2.output
+    output1.length == output2.length && output1.zip(output2).forall {
+      case (a1, a2) => a1.semanticEquals(a2)
+    }
+  }
 }