Return the XML element given the xpath expression.

Example:
| ${first_book}= | `Get XML XPath Element` | //catalog/book[1] | # This is similar to specifying "//catalog/book" as xpathExpression since this will only return a single element |

Result:
| ${first_book} =
| Element [0]:
| <book id="bk101">
|   <author>Gambardella, Matthew</author>
|   <title>XML Developer's Guide</title>
|   <genre>Computer</genre>
|   <price>44.95</price>
|   <publish_date>2000-10-01</publish_date>
|   <description>An in-depth look at creating applications with XML.</description>
| </book>