[9.x] Improve Collection's callable default return types

[MatanYadaev]

Currently, Collection methods that have a default parameter return incorrect type when the default parameter value is a closure.

The methods are:

• Collection::first
• Collection::last
• Collection::get
• Collection::pull
• LazyCollection::first
• LazyCollection::last
• LazyCollection::get

Code example:

$users = User::get();

// `$user1` is `User|null` - works well
$user1 = $user->get(key: 0);

// `$user2` is `User` - works well
$user2 = $user->get(key: 0, default: new User());

// `$user3` is `User|(Closure(): User)` - the type isn't correct
$user3 = $user->get(key: 0, default: function () {
  return new User();
});

After this PR:

// `$user4` is `User`
$user4 = $user->get(key: 0, default: function () {
  return new User();
});

[nunomaduro]

Thank you for this pull request. Feedback that must be addressed before merging:

• Please replace callable by \Closure.
• Please adjust the types on the interface `Illuminate\Support\Enumerable'.

[MatanYadaev]

@nunomaduro Thanks for the review. Done.

[driesvints]

Hi there, we've temporarily disabled our PostgreSQL build until we've managed to fix it. I've marked your PR as draft for now. Please rebase with master and mark this PR as ready when all tests pass again. Thanks.

[driesvints]

@MatanYadaev you incorrectly rebased this PR, causing some commits to duplicate. Luckily this PR was squash-merged. Please be mindful when rebasing PR's to avoid this as this can cause real-havoc on projects.