Named arguments
-----
<?php
foo(
    a: $b,
);
-----
$stmts[0]->expr->args[0]->name = null;
-----
<?php
foo(
    $b,
);
-----
<?php
foo(
    $b,
);
-----
$stmts[0]->expr->args[0]->name = new Node\Identifier('a');
-----
<?php
foo(
    a: $b,
);
-----
<?php
foo(
    a:
    $b,
);
-----
$stmts[0]->expr->args[0]->name = new Node\Identifier('XYZ');
-----
<?php
foo(
    XYZ:
    $b,
);