Describe the bug
If you try to get the declaration name of an arrow function using the method File::getDeclarationName(), it will throws an exception.

It looks like it is legit to use the method for a closure, since there is this condition here, so probably the same condition should be added also for T_FN.

Custom code sniff sample

use PHP_CodeSniffer\Sniffs\Sniff; use PHP_CodeSniffer\Files\File; class MyCustomCodeSniff implements Sniff { public function register() { return [T_FUNCTION, T_CLOSURE, T_FN]; } public function process(File $file, $position) { /** @var array<int, array<string, mixed>> $tokens */ $tokens = $file->getTokens(); if (!in_array(($tokens[$position]['code'] ?? null), [T_FUNCTION, T_CLOSURE, T_FN], true)) { return; } $functionStart = (int)($tokens[$position]['scope_opener'] ?? 0); $functionEnd = (int)($tokens[$position]['scope_closer'] ?? 0); if (($functionStart < 0) || ($functionEnd <= 0)) { return; } $declarationName = $file->getDeclarationName($position); // ... do other thins here ... } }

To reproduce
Steps to reproduce the behavior:

1. Create a file called test.php which contain a simple fn() => 'x';
2. Add the custom sniff rule
3. Run phpcs test.php ...
4. See error message displayed

An error occurred during processing; checking has been aborted. The error message was: Token type "T_FN" is not T_FUNCTION, T_CLASS, T_INTERFACE, T_TRAIT or T_ENUM (Internal.Exception) 

Expected behavior
A condition for T_FN is added as explained above, so that the method File::getDeclarationName() can return null instead of throwing an exception, when used on an arrow function.

Versions (please complete the following information):

• OS: MacOS 13.1
• PHP: 7.4
• PHPCS: 3.7.2
• Standard: