PHPCSStandards / PHP_CodeSniffer / 8791384934

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Tokenizer/PHP: arrow function tokenization broken when true/false used in return type

Since PHP 8.0, `false` and `null` can be included in a union return type.
As of PHP 8.2, both `true`, `false` and `null` can be used as a stand-alone return type.

The tokenizer layer handling arrow functions did not take this into account correctly. While `null` was handled correctly, `true` and `false` was not and would result in the arrow function `fn` keyword being tokenized as `T_STRING` across all PHP versions.
As a result of that, the other typical tokenizer changes related to arrow functions (`=>` as `T_FN_ARROW`, scope/parenthesis owners etc) would also not be executed correctly.

In practice, I suspect few people will have run into this bug as, after all, what's the point of declaring an arrow function which will only ever return `true` or `false` ? so in practice, it is likely to only have come into play for people using `true` or `false` as part of an arrow function union type.
All the same, PHPCS should handle this correctly.

Includes unit tests proving the bug and safeguarding the fix.

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