[8.x] Fix unvalidated array keys without implicit attributes

[bonroyage]

This PR aims to fix an issue that occurs when, in combination with the excludeUnvalidatedArrayKeys option on the validator, the array under validation does not have any implicit attributes. For example user.name instead of users.*.name.

This is fixed by also checking the keys present in getRules() instead of just the $implicitAttributes. As a result, the regex had to be altered slightly to check for the presence of at least one . following the attribute key. Otherwise it would not return anything when using just array without nested rules.

Validator::make([
    'admin' => ['name' => 'Mohamed', 'location' => 'cairo'], 
    'users' => [['name' => 'Mohamed', 'location' => 'cairo']]
], [
    'admin' => 'array',
    'admin.name' => 'string',
    'users' => 'array',
    'users.*.name' => 'string'
]);