Allow iteration blocks to have an optional extra index parameter (alternative to -n flags) (#6994)

Alters `all`, `any`, `each while`, `each`, `insert`, `par-each`, `reduce`, `update`, `upsert` and `where`,
so that their blocks take an optional parameter containing the index.

crates/nu-command/tests/commands/insert.rs

@@ -14,6 +14,15 @@ fn insert_the_column() {
     assert_eq!(actual.out, "0.7.0");
 }
 
+#[test]
+fn doesnt_convert_record_to_table() {
+    let actual = nu!(
+        cwd: ".", r#"{a:1} | insert b 2 | to nuon"#
+    );
+
+    assert_eq!(actual.out, "{a: 1, b: 2}");
+}
+
 #[test]
 fn insert_the_column_conflict() {
     let actual = nu!(
@@ -76,3 +85,13 @@ fn insert_past_end_list() {
 
     assert_eq!(actual.out, r#"[1,2,3,null,null,"abc"]"#);
 }
+
+#[test]
+fn uses_optional_index_argument() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"[[a]; [7] [6]] | insert b {|el ind| $ind + 1 + $el.a } | to nuon"#
+    ));
+
+    assert_eq!(actual.out, "[[a, b]; [7, 8], [6, 8]]");
+}