[12.x] Adds firstValue() to Collection

[DarkGhostHunter]

What?

This PR enables allows to return a value from the first element given the value is not null.

use App\Models\User;

$users = User::query()->limit(10)->get();

// before
$name = $users->firstWhere(function (User $user) {
    return $user->premium_since->isFuture();
})?->name

// after
$name = $users->firstValue(function (User $user) {
    if ($user->premium_since->isFuture()) {
        return $user->name;
    }
})

The idea of this PR is to avoid adding a ?->something at the end of the firstWhere, because sometimes adding a small tail to a code like this may be ignored by mistake.

[taylorotwell]

The "before" looks kinda fine to me? 😅

[DarkGhostHunter]

The "before" looks kinda fine to me? 😅

Are you sure? 🙃