Make query xml return nodes in document order (#13047)

# Description

`query xml` used to return results from an XPath query in a random,
non-deterministic order. With this change, results get returned in the
order they appear in the document.

# User-Facing Changes
`query xml` will now return results in a non-random order.

# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

crates/nu_plugin_query/src/query_xml.rs

@@ -88,7 +88,7 @@ pub fn execute_xpath_query(
 
             match r {
                 sxd_xpath::Value::Nodeset(ns) => {
-                    for n in ns.into_iter() {
+                    for n in ns.document_order() {
                         record.push(key.clone(), Value::string(n.string_value(), call.head));
                     }
                 }