Handle multiple Doctrine managers

[Mika56]

This is a merge request trying to solve #53
This is a work in progress, your contributions are welcome!

I've pushed a first proof of concept for now, there's still a lot to do:

• Completely remove ObjectMetadataResolver::getObjectManager() in favor of ObjectMetadataResolver::getObjectManagerForClass(). Remaining usages:
  • DqlRule::processNode line 57
  • QueryBuilderDqlRule::processNode line 80
  • QueryBuilderGetQueryDynamicReturnTypeExtension::getTypeFromMethodCall line 71
  • ExpressionBuilderDynamicReturnTypeExtension::getTypeFromMethodCall line 71
• There is not tests for setting an AbstractManagerRegistry instead of an ObjectManager for parameters.doctrine.objectManagerLoader
• We might want to use another parameter as to not introduce confusion

With these changes, PHPStan is capable of analyzing simple code that uses multiple managers

[ondrejmirtes]

The hard questions are:

1. What EM should we choose for DQL? How are DQL/QueryBuilders called when using ManagerRegistry in Doctrine in general?
2. What should we do when the user provides ManagerRegistry to PHPStan but in code we get EntityManager without any context?

[ondrejmirtes]

Please open a new PR if you decide to work on this again. Thanks.