Support redirect stderr and stdout+stderr with a pipe (#11708)

# Description
Close: #9673
Close: #8277
Close: #10944

This pr introduces the following syntax:
1. `e>|`, pipe stderr to next command. Example: `$env.FOO=bar nu
--testbin echo_env_stderr FOO e>| str length`
2. `o+e>|` and `e+o>|`, pipe both stdout and stderr to next command,
example: `$env.FOO=bar nu --testbin echo_env_mixed out-err FOO FOO e+o>|
str length`

Note: it only works for external commands. ~There is no different for
internal commands, that is, the following three commands do the same
things:~ Edit: it raises errors if we want to pipes for internal
commands
``` 
❯ ls e>| str length
Error:   × `e>|` only works with external streams
   ╭─[entry #1:1:1]
 1 │ ls e>| str length
   ·    ─┬─
   ·     ╰── `e>|` only works on external streams
   ╰────

❯ ls e+o>| str length
Error:   × `o+e>|` only works with external streams
   ╭─[entry #2:1:1]
 1 │ ls e+o>| str length
   ·    ──┬──
   ·      ╰── `o+e>|` only works on external streams
   ╰────
```

This can help us to avoid some strange issues like the following:

`$env.FOO=bar (nu --testbin echo_env_stderr FOO) e>| str length`

Which is hard to understand and hard to explain to users.

# User-Facing Changes
Nan

# Tests + Formatting
To be done

# After Submitting
Maybe update documentation about these syntax.

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

@@ -60,6 +60,26 @@ fn let_pipeline_redirects_externals() {
     assert_eq!(actual.out, "3");
 }
 
+#[test]
+fn let_err_pipeline_redirects_externals() {
+    let actual = nu!(
+        r#"let x = with-env [FOO "foo"] {nu --testbin echo_env_stderr FOO e>| str length}; $x"#
+    );
+
+    // have an extra \n, so length is 4.
+    assert_eq!(actual.out, "4");
+}
+
+#[test]
+fn let_outerr_pipeline_redirects_externals() {
+    let actual = nu!(
+        r#"let x = with-env [FOO "foo"] {nu --testbin echo_env_stderr FOO o+e>| str length}; $x"#
+    );
+
+    // have an extra \n, so length is 4.
+    assert_eq!(actual.out, "4");
+}
+
 #[ignore]
 #[test]
 fn let_with_external_failed() {