Pipeline blocks (#1579)

* Making Commands match what UntaggedValue needs

* WIP

* WIP

* WIP

* Moved to expressions for conditions

* Add 'each' command to use command blocks

* More cleanup

* Add test for 'each'

* Instead use an expression block

crates/nu-cli/tests/commands/each.rs

@@ -0,0 +1,13 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn each_works_separately() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+        echo [1 2 3] | each { echo $it 10 | sum } | to-json | echo $it
+        "#
+    ));
+
+    assert_eq!(actual, "[11,12,13]");
+}

crates/nu-cli/tests/commands/mod.rs

@@ -4,6 +4,7 @@ mod cd;
 mod compact;
 mod cp;
 mod default;
+mod each;
 mod edit;
 mod enter;
 mod first;