Add subcommands. Switch from-* and to-* to them (#1708)

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

@@ -5,7 +5,7 @@ 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
+        echo [1 2 3] | each { echo $it 10 | sum } | to json | echo $it
         "#
     ));