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

[michaelnabil230]

The feature adds the ability to have $perPage as a callback closure with access to $total.

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

// Now (saves extra query and builder code):
DB::table('products')->simplePaginate(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.

For example, in a list of products, with the above snippet, it will load all ~110 products if there are less than 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 on the second page.

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

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

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

This PR is a same this PR #42429 put in simplePaginate

[taylorotwell]

This seems to break the simple pagination concept in general - you are running a count.