Do not error if a non-field findByX method exists

[roverwolf]

Do not generate an error if a custom findByX (or findOneByX, countByX) method exists but X is not a field in the entity class.

This should fix #52

[ondrejmirtes]

Hi, this isn't sufficient.

1. There's no test that reproduces the problem.
2. PHPStan's reflection objects should be used - you can obtain them by injecting Broker into the rule and calling $this->broker->getClass() and then ask for hasNativeMethod.
3. There are multiple places that need to be fixed (and all of those bugs need to be reproduced first with tests):

• https://github.com/phpstan/phpstan-doctrine/blob/master/src/Type/Doctrine/ObjectRepositoryDynamicReturnTypeExtension.php
• https://github.com/phpstan/phpstan-doctrine/blob/master/src/Rules/Doctrine/ORM/MagicRepositoryMethodCallRule.php

[roverwolf]

I've added a test and changed to use PHPStan's Broker (sorry, I am new to PHPStan).

I have not seen any errors from PHPStan due to ObjectRepositoryDynamicReturnTypeExtension. Does it need to change if we assume the rule stays the same where a "find" method should return the entity class (or null, or an array of them)?

[ondrejmirtes]

I'll look at ObjectRepositoryDynamicReturnTypeExtension myself. Thank you!