Use the APIs for creation from utf8 string. (#2506)

Signed-off-by: Firestarman <firestarmanllc@gmail.com>

sql-plugin/src/main/scala/com/nvidia/spark/rapids/literals.scala

@@ -110,9 +110,7 @@ object GpuScalar extends Arm with Logging {
   /** Converts an element for nested lists */
   private def convertElementTo(element: Any, elementType: DataType): Any = elementType match {
     case _ if element == null => null
-    // StructData does not support utf8 string yet, so parses it here instead of calling the
-    //  `convertUTF8StringTo`. Tracked by https://github.com/rapidsai/cudf/issues/8137
-    case StringType => element.asInstanceOf[UTF8String].toString
+    case StringType => element.asInstanceOf[UTF8String].getBytes
     case dt: DecimalType => convertDecimalTo(element.asInstanceOf[Decimal], dt) match {
       case Left(i) => i
       case Right(l) => l
@@ -159,13 +157,10 @@ object GpuScalar extends Arm with Logging {
       case TimestampType =>
         ColumnVector.timestampMicroSecondsFromBoxedLongs(seq.asInstanceOf[Seq[JLong]]: _*)
       case StringType =>
-        // To be updated. https://github.com/rapidsai/cudf/issues/8137
-        ColumnVector.build(DType.STRING, seq.length, b => {
-          seq.asInstanceOf[Seq[UTF8String]].foreach {
-            case null => b.appendNull()
-            case s => b.appendUTF8String(s.getBytes)
-          }
-        })
+        ColumnVector.fromUTF8Strings(seq.asInstanceOf[Seq[UTF8String]].map {
+          case null => null
+          case us => us.getBytes
+        }: _*)
       case dt: DecimalType =>
         val decs = seq.asInstanceOf[Seq[Decimal]]
         if (DecimalType.is32BitDecimalType(dt)) {
@@ -290,8 +285,7 @@ object GpuScalar extends Arm with Logging {
     }
     case StringType => v match {
       case s: String => Scalar.fromString(s)
-      // TODO JNI supports creating a scalar from UTF8 String bytes directly.
-      case us: UTF8String => Scalar.fromString(us.toString)
+      case us: UTF8String => Scalar.fromUTF8String(us.getBytes)
       case _ => throw new IllegalArgumentException(s"'$v: ${v.getClass}' is not supported" +
         s" for StringType, expecting String or UTF8String.")
     }