[SPARK-32090][SQL] Improve UserDefinedType.equal() to make it be symmetrical

### What changes were proposed in this pull request?

This PR fix `UserDefinedType.equal()` by comparing the UDT class instead of checking `acceptsType()`.

### Why are the changes needed?

It's weird that equality comparison between two UDT types can have different result by switching the order:

```scala
// ExampleSubTypeUDT.userClass is a subclass of ExampleBaseTypeUDT.userClass
val udt1 = new ExampleBaseTypeUDT
val udt2 = new ExampleSubTypeUDT
println(udt1 == udt2) // true
println(udt2 == udt1) // false
```

### Does this PR introduce _any_ user-facing change?

Yes.

Before:
```scala
// ExampleSubTypeUDT.userClass is a subclass of ExampleBaseTypeUDT.userClass
val udt1 = new ExampleBaseTypeUDT
val udt2 = new ExampleSubTypeUDT
println(udt1 == udt2) // true
println(udt2 == udt1) // false
```

After:
```scala
// ExampleSubTypeUDT.userClass is a subclass of ExampleBaseTypeUDT.userClass
val udt1 = new ExampleBaseTypeUDT
val udt2 = new ExampleSubTypeUDT
println(udt1 == udt2) // false
println(udt2 == udt1) // false
```

### How was this patch tested?

Added a unit test.

Closes apache#28923 from Ngone51/fix-udt-equal.

Authored-by: yi.wu <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: Ngone51

sql/catalyst/src/main/scala/org/apache/spark/sql/types/UserDefinedType.scala

@@ -90,7 +90,7 @@ abstract class UserDefinedType[UserType >: Null] extends DataType with Serializa
   override def hashCode(): Int = getClass.hashCode()
 
   override def equals(other: Any): Boolean = other match {
-    case that: UserDefinedType[_] => this.acceptsType(that)
+    case that: UserDefinedType[_] => this.getClass == that.getClass
     case _ => false
   }
 

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

@@ -134,6 +134,24 @@ class UserDefinedTypeSuite extends QueryTest with SharedSparkSession with Parque
     MyLabeledPoint(1.0, new TestUDT.MyDenseVector(Array(0.1, 1.0))),
     MyLabeledPoint(0.0, new TestUDT.MyDenseVector(Array(0.3, 3.0)))).toDF()
 
+
+  test("SPARK-32090: equal") {
+    val udt1 = new ExampleBaseTypeUDT
+    val udt2 = new ExampleSubTypeUDT
+    val udt3 = new ExampleSubTypeUDT
+    assert(udt1 !== udt2)
+    assert(udt2 !== udt1)
+    assert(udt2 === udt3)
+    assert(udt3 === udt2)
+  }
+
+  test("SPARK-32090: acceptsType") {
+    val udt1 = new ExampleBaseTypeUDT
+    val udt2 = new ExampleSubTypeUDT
+    assert(udt1.acceptsType(udt2))
+    assert(!udt2.acceptsType(udt1))
+  }
+
   test("register user type: MyDenseVector for MyLabeledPoint") {
     val labels: RDD[Double] = pointsRDD.select('label).rdd.map { case Row(v: Double) => v }
     val labelsArrays: Array[Double] = labels.collect()