Return the XML element text content given the xpath expression.

Example:
| ${third_book}= | `Get XML XPath Element` | //catalog/book[3] |
| ${genre}= | `Get XML XPath Element Text Content` | ${third_book} | //book/genre |  # This is similar to specifying "book/genre" as xpathExpression assumes book on the root element. |

Result:
| ${genre} = Fantasy