More fine-grained control for Inertia::merge() and a new Inertia::scroll()

[pascalbaljet]

This PR provides a new middle ground between Inertia::merge() and Inertia::deepMerge() so you can have fine-grained control over what should be merged.

In this example, the front-end will replace the entire object, except the data array. The new items will be appended to the existing items.

Inertia::merge(User::paginate())->append('data');

There's also prepend(), and you can also combine multiple calls.

Inertia::merge($complexObject)
    ->append('users', matchOn: 'username')
    ->prepend('messages.data');

You can pass arrays.

Inertia::merge($complexObject)->append(['users', 'messages']);

And even pass a key-value array where the key is the path, and the value the matchOn.

Inertia::merge($complexObject)->append([
    'users.data' => 'id',
    'messages' => 'uuid',
]);

Then there's a new Inertia::scroll() function which you can pass paginated resources.

Inertia::scroll(User::paginate());

In addition to automatically calling append('data') or prepend('data') for you, it sends normalized pagination metadata to the front-end, no matter if you use simple/cursor/full pagination, even wrapped within an Eloquent API resource.

Draft because the tests and front-end PR are not ready yet.

Fixes #762.
See also: inertiajs/inertia#2561