minor #48793 Leverage arrow function syntax for closure (tigitz)

This PR was merged into the 6.3 branch.

Discussion
----------

Leverage arrow function syntax for closure

| Q             | A
| ------------- | ---
| Branch?       | 6.3
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | Fix #47658 <!-- prefix each issue number with "Fix #", no need to create an issue if none exists, explain below instead -->
| License       | MIT
| Doc PR        | <!-- required for new features -->

Rationale in the RFC [here](https://wiki.php.net/rfc/arrow_functions_v2#introduction)

It's also notable that using arrow function syntax rather than the classic one has been enforced in the past by symfony core member: symfony/symfony#48069 (comment)

So this PR would be consistent.

Commits
-------

f5802d3a2a Leverage arrow function syntax for closure

Node/FunctionNode.php

@@ -64,9 +64,7 @@ public function getSpecificity(): Specificity
 
     public function __toString(): string
     {
-        $arguments = implode(', ', array_map(function (Token $token) {
-            return "'".$token->getValue()."'";
-        }, $this->arguments));
+        $arguments = implode(', ', array_map(fn (Token $token) => "'".$token->getValue()."'", $this->arguments));
 
         return sprintf('%s[%s:%s(%s)]', $this->getNodeName(), $this->selector, $this->name, $arguments ? '['.$arguments.']' : '');
     }

Parser/Parser.php

@@ -57,9 +57,7 @@ public static function parseSeries(array $tokens): array
             }
         }
 
-        $joined = trim(implode('', array_map(function (Token $token) {
-            return $token->getValue();
-        }, $tokens)));
+        $joined = trim(implode('', array_map(fn (Token $token) => $token->getValue(), $tokens)));
 
         $int = function ($string) {
             if (!is_numeric($string)) {

Tests/Parser/ParserTest.php

@@ -25,9 +25,7 @@ public function testParser($source, $representation)
     {
         $parser = new Parser();
 
-        $this->assertEquals($representation, array_map(function (SelectorNode $node) {
-            return (string) $node->getTree();
-        }, $parser->parse($source)));
+        $this->assertEquals($representation, array_map(fn (SelectorNode $node) => (string) $node->getTree(), $parser->parse($source)));
     }
 
     /** @dataProvider getParserExceptionTestData */