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

``` php
$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.