[9.x] Added Eloquent withWhereHas method

[eusonlito]

There are a lot of times that we need to load a relationship using with with the same conditions that we use for whereHas.

This method simplifies this selection by avoiding repeating the code used both to filter with whereHas and then to select that same record using with. There is less code, it is more readable and easier to maintain.

Before

CollectionModel::whereHas('products', function ($query) {
    $query->where('enabled', true)->where('sale', true);
})->with(['products' => function ($query) {
    $query->where('enabled', true)->where('sale', true);
});

After

CollectionModel::withWhereHas('products', fn ($query) => $query->where('enabled', true)->where('sale', true));

If it's ok for you, I will add tests :)

[taylorotwell]

I think it seems pretty decent if you want to add tests. Mark as ready for review when done.

[lovemintblue]

nice！