[9.x] Adds ability to have paginate() $perPage parameter as callable with access to $total

[Niush]

Feature adds ability to have $perPage as a callback closure with access to $total.

// Previously:
$total = DB::table('products')->count();
DB::table('products')->paginate( $total <= 110 ? 110 : 100 );

// Now (saves extra query and builder code):
DB::table('products')->paginate(function ($total) {
    return $total <= 110 ? 110 : 100;
});

There might be a scenario when you want to use different/dynamic per page depending on the total count of records.

Example, in a list of products, with above snippet, it will load all ~110 products if there is less then or equal to 110 products in total. Else, defaults to 100 as usual. So that, there won't be just a few items sitting around in second page.

Similarly, if we want to have exact 4 pages, we can provide dynamic per page value like such:

Product::oldest()->paginate(function ($total) {
    return ceil($total / 4); // Will always have at most 4 pages in total
});

And, of course the normal paginate(10) will still work.

[johanrosenson]

Nitpicking, but your last example need to use ceil instead of round to get at most 4 pages, otherwise something like total = 101 will be 5 pages.