?:array has item ?:array in key path ?:string

[elliotchance]

$a = [
    'foo' => [
        'abc' => [
            [ 'bar' => 'baz' ],
        ],
    ],
];

$this->assert($a, has_item, [ 'bar' => 'baz' ], in_key_path, 'foo.abc');

This should also apply to finding keys and values.