[12.x] Add mergeHidden and mergeVisible methods to Collection class

[mahmoudmohamedramadan]

This PR extends the mergeHidden and mergeVisible methods to Eloquent Collections, allowing you to adjust attribute visibility across an entire collection—not just individual models.

use App\Models\User;

$users = User::withWhereHas('comments')->get();

$users->mergeVisible(['updated_at']);