[6.x] Override BelongsToMany::cursor() to hydrate pivot relations

[mpyw]

Overview

Currently pivot relations are not hydrated over cursor() request. We need to override it like each() chunk() chunkById() paginate() simplePaginate().

foreach (Post::first()->tags()->cursor() as $tag) {
    dump($tag->pivot->flag); // This cannot be correctly retrieved now
}

It seems that HasManyThrough::cursor() is already correctly implemented.

Related PRs

• [5.7] Fix each() on BelongsToMany relationships by staudenmeir · Pull Request #25832 · laravel/framework
• [5.6] Fix for HasManyThrough returning incorrect results with chunk()… by AmmarRahman · Pull Request #24096 · laravel/framework
• [5.0] Eloquent belongsToMany chunk by codelight89 · Pull Request #8045 · laravel/framework