Make semicolon works better for internal commands (#6643)

* make semicolon works with some internal command like do

* refactor, make consume external result logic out of eval_external

* update comment

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

@@ -11,3 +11,15 @@ fn capture_errors_works() {
 
     assert_eq!(actual.out, "error");
 }
+
+#[test]
+fn do_with_semicolon_break_on_failed_external() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        do { nu --not_exist_flag }; `text`
+        "#
+    ));
+
+    assert_eq!(actual.out, "");
+}