minor #9764 [ExpressionLanguage] Add missing argument in example code (kevin-verschaeve, javiereguiluz)

This PR was submitted for the 2.7 branch but it was merged into the 2.8 branch instead (closes #9764).

Discussion
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[ExpressionLanguage] Add missing argument in example code

Like the docs says just below
>  Both the compiler and evaluator are passed an arguments variable as their first argument

The example was missing the `$arguments` for the `compiler` method

Commits
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280c23c Reword
3ce4089 [ExpressionLanguage] Add missing argument in example code

Author: javiereguiluz

components/expression_language/extending.rst

@@ -45,11 +45,11 @@ This method has 3 arguments:
     });
 
     var_dump($expressionLanguage->evaluate('lowercase("HELLO")'));
+    // this will print: hello
 
-This will print ``hello``. Both the **compiler** and **evaluator** are passed
-an ``arguments`` variable as their first argument, which is equal to the
-second argument to ``evaluate()`` or ``compile()`` (e.g. the "values" when
-evaluating or the "names" if compiling).
+In addition to the custom function arguments, the **evaluator** is passed an
+``arguments`` variable as its first argument, which is equal to the second
+argument of ``compile()`` (e.g. the "values" when evaluating an expression).
 
 .. _components-expression-language-provider: