Fixes #14188: Add constants and function for sysexits(3) to ConsoleHelper

docs/guide/tutorial-console.md

@@ -267,12 +267,21 @@ public function actionIndex()
 }
 ```
 
-There are some predefined constants you can use:
+There are some predefined constants you can use. These are defined in the [[yii\console\ExitCode]] class:
 
-- [[yii\console\Controller::EXIT_CODE_NORMAL|Controller::EXIT_CODE_NORMAL]] with value of `0`;
-- [[yii\console\Controller::EXIT_CODE_ERROR|Controller::EXIT_CODE_ERROR]] with value of `1`.
+```php
+public function actionIndex()
+{
+    if (/* some problem */) {
+        echo "A problem occurred!\n";
+        return ExitCode::UNSPECIFIED_ERROR;
+    }
+    // do something
+    return ExitCode::OK;
+}
+```
 
-It's a good practice to define meaningful constants for your controller in case you have more error code types.
+It's a good practice to define meaningful constants for your controller in case you have more specific error code types.
 
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