LibJS: Fix arrow function parsing bug

In the following example:
```js
const f = (i) => ({
    obj: { a: { x: i }, b: { x: i } },
    g: () => {},
});
```

The body of function `f` is initially parsed as an arrow function. As a
result, what is actually an object expression is interpreted as a formal
parameter with a binding pattern. Since duplicate identifiers are not
allowed in this context (`i` in the example), the parser generates an
error, causing the entire script to fail parsing.

This change ignores the "Duplicate parameter names in bindings" error
during arrow function parameter parsing, allowing the parser to continue
and recognize the object expression of the outer arrow function with an
implicit return.

Fixes error on https://chat.openai.com/

Libraries/LibJS/Parser.cpp

@@ -1065,8 +1065,12 @@ RefPtr<FunctionExpression const> Parser::try_parse_arrow_function_expression(boo
 
             auto const_correct_parameters = parse_formal_parameters(function_length, FunctionNodeParseOptions::IsArrowFunction | (is_async ? FunctionNodeParseOptions::IsAsyncFunction : 0));
             parameters = fixme_launder_const_through_pointer_cast(const_correct_parameters);
-            if (m_state.errors.size() > previous_syntax_errors && m_state.errors[previous_syntax_errors].message.bytes_as_string_view().starts_with("Unexpected token"sv))
-                return nullptr;
+            if (m_state.errors.size() > previous_syntax_errors) {
+                auto error_message = m_state.errors[previous_syntax_errors].message.bytes_as_string_view();
+                if (error_message.starts_with("Unexpected token"sv) || error_message.starts_with("Duplicate parameter names"sv)) {
+                    return nullptr;
+                }
+            }
             if (!match(TokenType::ParenClose))
                 return nullptr;
             consume();

Libraries/LibJS/Tests/syntax/return-object-with-duplicated-field-names-from-arrow-function.js

@@ -0,0 +1,10 @@
+test("returning object with duplicated member names (i) should not throw exception", () => {
+    expect(`
+const f = (i) => ({
+    obj: { a: { x: i }, b: { x: i } },
+    g: () => {},
+});
+
+f(123);
+    `).toEval();
+});