[6.x] Add support for nested arrays with assertViewHas

[owenconti]

This PR adds nested array support to the assertViewHas method.

Here's an example of the before/after usage:

// controller

return Inertia::render('PageComponent', [
    'user_name' => 'John Doe'
]);

Testing before PR:

// test class

$this->get('/page')
    ->assertViewHas('page', [
        'component' => 'PageComponent',
        'url' => '/page',
        'version' => null,
        'props' => [
            'user_name' => 'John Doe'
        ]
    ]);

Testing after PR:

$this->get('/page')
    ->assertViewHas('page.props', [
        'user_name' => 'John Doe'
    ]);

So in this example, I'm using Inertia to render a page. Inertia attaches multiple "props" to the page key passed to the view. I only really care to test that the data I returned from my controller is set correctly.

I think this could be useful for usage outside of Inertia as well, where a controller may return nested data to a view and a test wants to pick out a nested key.

I've also added a couple extra tests that were missing for assertViewHas.