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/update.rs

@@ -14,6 +14,15 @@ fn sets_the_column() {
     assert_eq!(actual.out, "0.7.0");
 }
 
+#[test]
+fn doesnt_convert_record_to_table() {
+    let actual = nu!(
+        cwd: ".", r#"{a:1} | update a 2 | to nuon"#
+    );
+
+    assert_eq!(actual.out, "{a: 2}");
+}
+
 #[cfg(features = "inc")]
 #[test]
 fn sets_the_column_from_a_block_run_output() {
@@ -105,3 +114,13 @@ fn update_nonexistent_column() {
 
     assert!(actual.err.contains("cannot find column 'b'"));
 }
+
+#[test]
+fn uses_optional_index_argument() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"[[a]; [7] [6]] | update a {|el ind| $ind + 1 + $el.a } | to nuon"#
+    ));
+
+    assert_eq!(actual.out, "[[a]; [8], [8]]");
+}