[SPARK-51784] Support xml in DataFrame(Reader/Writer)

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to support xml API in DataFrameReader and DataFrameWriter.

Why are the changes needed?

xml API is newly added at Apache Spark 4.0.0. We had better support this for the feature parity.

https://github.com/apache/spark/blob/e0801d9d8e33cd8835f3e3beed99a3588c16b776/sql/api/src/main/scala/org/apache/spark/sql/DataFrameReader.scala#L394-L403

  /**
   * Loads a XML file and returns the result as a `DataFrame`. See the documentation on the other
   * overloaded `xml()` method for more details.
   *
   * @since 4.0.0
   */
  def xml(path: String): DataFrame = {
    // This method ensures that calls that explicit need single argument works, see SPARK-16009
    xml(Seq(path): _*)
  }

Does this PR introduce any user-facing change?

No, this is a new addition.

How was this patch tested?

Pass the CIs.

Was this patch authored or co-authored using generative AI tooling?

No.

[dongjoon-hyun]

Thank you, @viirya . Merged to main.