Fixes #55026.

• For updateExistingPivot, there is no extra cost in terms of performance; it's already sending a database query for fetching data when using the updateExistingPivot method for custom classes. (InteractsWithPivotTable.php#L242)
• For detach, a query like updateExistingPivot will be run before deleting, only if the user uses a custom pivot class and withPivotValue (or wherePivot), otherwise, it's working exactly as it was working before.
• The previous version of updateExistingPivot used the collection where method instead of query builder where method, so I added a new method to get currently attached pivot models with related keys filter, so the where method will run by query builder instead of collection for better performance and not fetching data that is not needed for update/delete pivots.