Support for disabling automatic escaping in to xml (#11536)

# Description
This PR addresses #11525 by adding `--partial-escape` which makes `to
xml` only escape `<>&` in text and `<>&"` in comments. This PR also
fixes issue where comment and PI content was escaped even though [it
should not be](https://stackoverflow.com/a/46637835)

# User-Facing Changes
Correct comments and PIs
 `to xml --partial-escape` flag to emit less escaped characters

# Tests + Formatting
Added tests for specified issues

crates/nu-command/tests/format_conversions/xml.rs

@@ -58,3 +58,36 @@ fn to_xml_error_tag_not_string() {
 
     assert!(actual.err.contains("not a string"));
 }
+
+#[test]
+fn to_xml_partial_escape() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            {
+                tag: a
+                attributes: { a: "'a'\\" }
+                content: [ `'"qwe\` ]
+            } | to xml --partial-escape
+        "#
+    ));
+    assert_eq!(actual.out, r#"<a a="'a'\">'"qwe\</a>"#);
+}
+
+#[test]
+fn to_xml_pi_comment_not_escaped() {
+    // PI and comment content should not be escaped
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            {
+                tag: a
+                content: [
+                    {tag: ?qwe content: `"'<>&`}
+                    {tag: ! content: `"'<>&`}
+                ]
+            } | to xml
+        "#
+    ));
+    assert_eq!(actual.out, r#"<a><?qwe "'<>&?><!--"'<>&--></a>"#);
+}