[12.x] Add Eloquent Collection methods: setAppends && withoutAppends

[cosmastech]

I started a new job and some of the legacy code has models with appended attributes. In wanting to improve speed of tests, I have been refactoring pagination tests to leverage Model@fillAndInsert(). I was confused as to why the inserts were failing only to discover the appends properties were the root cause.

User::query()->fillAndInsert(
    User::factory()
        ->count(100)
        ->make()
        ->each(fn ($u) => $u->setAppends([]))
);

With this change, I can make this a bit cleaner:

User::query()->fillAndInsert(
    User::factory()
        ->count(100)
        ->make()
        ->withoutAppends()
);