[11.x] Adds support for enums on mapInto collection method

[lukeraymonddowning]

Hey all!

This PR adds backed enum support to the Collection::mapInto method. This essentially allows us to build up enums from an array of backing values.

A Sample Use Case

One use case for this is when dealing with an array of data passed from the front end.

public function store(Request $request)
{
    $request->validate([
        'features' => ['array'],
        'features.*' => [new Enum(Feature::class)],
    ]);

    $features = $request
        ->collect('features')
        ->mapInto(Feature::class);

    if ($features->contains(Feature::DarkMode)) {
        // 🌙
    }
}

Imagine that we have a Feature enum, and the frontend provides checkboxes for selecting from these features. Obviously, we can't send the enum case in the request, so we send the backing value of the enum instead. Using the updated mapInto method, we can easily transform those backing values into enum cases.

There we go, nothing major. Just felt it was a nice DX improvement and in my mind is what I'd expect when passing an enum to the mapInto method.

Thanks for all the hard work!

Kind Regards,
Luke