forceDelete on User prevented by Foreign Key Constraints

[claudious96]

When deleting a user from the admin panel, using the User model forceDelete option ($user->delete(true)), in the confirmation modal shows up an alert about a generic php error.
Seems like the foreign key constraints prevent the deletion of any activity related to the user.

For more insight see comments on #951.

My setups in which I reproduced the error:

• UF 4.2 (vanilla)
• OS Windows/Ubuntu 18.04
• Apache 2.4.37
• MariaDB 10.1.37 (tested also with MySql 5.7.25)
• PHP 7.3.0 (tested also with 7.2.15)

This fix worked in my case (all setups above successfully tested) and won't break any custom Sprinkle
First I defined the classMapping of the Persistence model inside ServicesProvider.php

$container->extend('classMapper', function ($classMapper, $c) {
           ...
            $classMapper->setClassMapping('persistence', 'UserFrosting\Sprinkle\Account\Database\Models\Persistence');

            return $classMapper;
        });

And then here is the edited delete method of the User model

public function delete($hardDelete = false)
    {
        /** @var \UserFrosting\Sprinkle\Core\Util\ClassMapper $classMapper */
        $classMapper = static::$ci->classMapper;

        if ($hardDelete) {
            // Remove all role associations
            $this->roles()->detach();

            static::$ci->db->schema()->disableForeignKeyConstraints();
            // Remove all user activities
            $classMapper->staticMethod('activity', 'where', 'user_id', $this->id)->delete();

            // Remove all user tokens
            $classMapper->staticMethod('password_reset', 'where', 'user_id', $this->id)->delete();
            $classMapper->staticMethod('verification', 'where', 'user_id', $this->id)->delete();
            $classMapper->staticMethod('persistence', 'where', 'user_id', $this->id)->delete();

            // Delete the user
            $result = $this->forceDelete();
            static::$ci->db->schema()->enableForeignKeyConstraints();
        } else {
            // Soft delete the user, leaving all associated records alone
            $result = parent::delete();
        }

        return $result;
    }

[lcharette]

Will be fixed in 4.2.1