[TypeDeclaration] Map accessory string intersection to string in union return type

[TomasVotruba]

Problem

ReturnUnionTypeRector failed to add a return type to methods like:

private function getAssetSize(): int { /* ... */ }

public function getTotalFilesize($assets)
{
    if (empty($assets)) {
        return 0;
    }

    $size = $this->getAssetSize($assets);

    if ($size) {
        $size = (string) $size;
    }

    return $size;
}

PHPStan infers the native return type as 0 | (numeric-string & non-falsy-string) — i.e. int | string. But IntersectionTypeMapper::mapToPhpParserNode() only handled object intersections; the string-accessory member (numeric-string & non-falsy-string) hit the ! $type instanceof ObjectType branch and returned null, which aborted the whole UnionTypeMapper. Net result: no return type was added at all.

Fix

A pure-string intersection is just string. Map it directly before the object handling:

if ($type->isString()->yes()) {
    return new Identifier('string');
}

Now the rule adds int|string as expected.

Test

Added fixture int_or_numeric_string.php.inc mirroring the real-world shape.